No – you must complete the specified number of sessions for each Challenge and race. For example, IRONMAN VR2 is 3 km run, 40 km bike, 10 km run. You cannot split up the bike into multiple sessions. You must complete 40 km in one session to be considered a finisher.
NB: there might be exceptions! Some of our VR accept an "unlimited number of sessions" to accumulate the distance to reach. It will always be specified in the text.