Each page within a FullStory session gets its page start time from FullStory recording servers. Because page start times originate from the recording servers, all FullStory sessions will be in sync, regardless of potential time variability in end users' browser clients. FullStory recording servers use Google Compute Engine instances, which in turn are synchronized using Network Time Protocol (NTP) to insure consistency across all server side nodes. This insures that all sessions should semantically flow in the actual order that they were recorded.
After page recording begins, all raw events captured on the client side within the end user's browser are recorded with a relative timestamp offset from the start of capture. This relative timestamp is then later applied to the server captured start time mentioned above to render the final time value displayed when watching a FullStory session.
FullStory sessions are always recorded in UTC time, but the time that shows up in the FullStory application is always displayed in the timezone of the user logged into the FullStory application. The timezone of the end user who was recorded is not present during session playback.
Switching to absolute time
You can switch between the relative and absolute time during during session playback by clicking on the the timestamp at the bottom: