Debriefing - is it best to do immediately after an IS, or would it be OK
to listen to the tape later on in the day and interpret it then?

A debrief is always done immediately after the experience. It's required by NASA, researchers and anyone who wants greater accuracy in their reports.

Reason being that emotional triggers that occured whilst image streaming will often cue you to the positive or negative implication of the words. Cold steel rod might be interpreted as an indifferent piece of metal or indifference however the shiver that went down your spine while you were descriving it would clearly change the message to mean something like cold dislike.

These subtle experiences are ofent so quick you might not have decribed it out loud but did notice it. By delaying the debrief these cues are forgetten or remembered differently or associated differently.
Alex