When does the Spirit separate from the Body?

From Kardec’s The Spirits' Book - Separation of the Soul and Body 

154. Is the separation of the soul from the body painful? 
“No, the body often suffers more during life than at death because the soul is usually unaware of what is occurring to the body at death.  At the time of death, the spirit often enjoys what it is feeling, because it recognizes that it is at the end of its exile.  In natural death (exhaustion of the body due to age), human beings depart this life without even realizing that they are doing so.”

155. How does the separation of the soul from the body take place? 
“As the bonds restraining the soul are broken, it separates from the body.” 

a) Is this separation sudden? Is there a distinct line between life and death? 
“No, it is not like a bird whose cage is suddenly opened allowing it to escape at once. The soul gradually separates from the body. The two states are blurred together and the spirit extracts itself little by little from its bonds, which are loosened but not broken.” 

During life, a spirit is connected to the body by its semi-material envelope, or perispirit. Death is the destruction of the body, but not of this envelope, which separates from the body when organic life ends. Observation has shown us that the separation of the perispirit from the body at death is gradual, rather than abrupt, and this speed may vary depending on different individuals. In some cases, it is so quick that the perispirit completely separates from the body within a few hours after passing, while in others, particularly for those whose life has been exceedingly material and sensual, this release is much slower, and can take days, weeks, and even months. This does not imply the continuance of vitality in the body or any possibility of restoring life, but is simply the result of a hold between the body and the spirit proportionate to how consumed the spirit was with materiality during its human life. It is only rational to assume that if a spirit has closely identified with matter, it will be more difficult for it to separate from its material body. In contrast, intellectual and moral elevation of thought initiates this division even during the life of the body. 

Consequently, when death ultimately arrives, the separation is almost immediate. Studies of individuals after their death have shown that sometimes, the connection that remains between the soul and the body is extremely painful, as the spirit is fully cognizant of all the horrors of decomposition. This is an exceptional case, and unique to certain kinds of life and certain kinds of death. It can happen in the event of suicide. 

156. Can the definitive separation of the soul and body take place before the complete termination of organic life? 
“When experiencing extreme agony, the soul sometimes leaves the body so that all that remains is purely organic life. The person is no longer conscious of him or herself, despite the faint flicker of vitality remaining. The body is a machine that is regulated by the heart. As long as the heart pumps blood through its veins it continues to live. A soul is not needed for this.” 

157. At the moment of death, does the soul sometimes experience a kind of bliss that gives it a glimpse of the world to which it is about to return to? 
“The soul often feels the slackening of the restraints holding it to the body, and struggles to fully break them. Partially freed from matter, it views the future laid out before it, and enjoys the anticipation of the spirit state.” 

159. How does the soul feel when it realizes that it is in the spirit world? 
“That depends. People who have done wrong for the sake of doing wrong feel overwhelmed by shame for their behavior. The soul of a righteous individual is at ease, as if a heavy weight has been lifted and does not dread even the most penetrating evaluation.” 

160. Are spirits immediately surrounded by people who they knew on Earth and died before them? 
“Yes, according to the degree of affection they had for them and vice versa. They often come to them upon their return to the spirit world and help them shed material ties. Others whom they formerly knew, but may have lost contact with on Earth, come to meet them as well. They see all who are wandering, and visit those who are still incarnated.” 

Spirit Confusion 

163. Does the soul immediately regain self-consciousness upon leaving the body? 
“Not immediately. It is in a state of confusion.” 

164. Do all spirits experience the confusion that follows the separation of the soul from the body to the same degree and for the same span of time? 
“No, this depends on their elevation. The person who is already purified recovers consciousness almost immediately, because they have already freed themselves from the shackles of materialism during physical life. However, a more materialistic person, whose conscience is not clear, remains branded with the impression of matter for a longer period of time.” 

165. Does the knowledge of Spiritism have any influence on the duration of this state of confusion? 
“It has a substantial influence on its duration, because the spirit acquired a prior understanding about its new situation. However, the practice of righteousness and a clear conscience have the most influence.” 

When death arrives, everything is chaotic at first. The soul is stunned, similar to when a person wakes from a deep sleep, and needs time to establish its bearings and fully comprehend the situation. It gradually regains clarity and the memory of the past as the influence of the material envelope that it has recently shed weakens, and the fog that obscured its consciousness clears. 
The duration of confusion following death varies greatly. It may be a few hours, several months, or even years. Those who, during their human lives, have closely identified themselves with their future state do not remain confused for long, because they are able to gain quicker understanding of their situation. 

This confusion is completely dependent on specific features, and the type of death. In cases of violent death, suicide, torture, accident, stroke, injuries, and so on, the spirit is shocked and does not believe that it is dead. It stubbornly maintains the contrary and views the body that it has left as something separate from itself. It recognizes its body and cannot understand how it could be separated from it. It remains among those it has loved, speaks to them, and does not understand why they do not hear it. This illusion lasts until the perispirit has fully separated from the physical body. It is only when this is accomplished that the spirit begins to understand that it no longer is part of the physical world. 

This phenomenon is easy to explain. With death occurring unexpectedly, the spirit is stunned by the sudden change that has taken place. Death is still equivalent to destruction for the spirit and it thinks that it cannot possibly be dead. This illusion is still further reinforced by seeing itself with a body similar to the one it has left, because it does not immediately perceive its ethereal (not composed of matter) nature and believes that it is solid, just as it was in the corporeal world. 
The confusion that follows death is in no way painful for people who have lived an honest life. They are calm and feel as if they are peacefully waking out of slumber. However, people whose conscience is not clear are brimming with anxiety and anguish and this only heightens as they gain full cognizance. 

In cases of a collective death, in which many individuals have died together in the same catastrophe, they do not always see one another immediately afterwards. Each spirit goes its own way in the confusion following death, or only worries about those in whom it takes an interest.