"Except for the basic time and effort required to undergo submersion tasks (see below), the gamemaster is free to adjust the time spent and the submersion event involved to suit the character and the flavour of her campaign. As the Resonance cyberspace is beyond the sense of time, characters could even experience a whole virtual life during a submersion."
- Unwired P141.
So really, it's up to you.
Also.
"Subjective time in the resonance realms almost always differs from real-world time, so that a trip that seems to last for 10 hours may in reality have taken only 10 minutes or, more drastically, 10 days. Some technomancers have been caught off-guard by this difference, their physical bodies nearly dying from dehydration or other factors while their minds were away."
- Unwired P173
It's a major thing to do. You have to confront your own demons more or less, and that's only after undergoing meditation to harmonise with the Resonance which takes a number of hours. That's just for going in and looking around, submerging yourself would take a bit longer. That said, make sure they do have the time to do it in such a way that submerging doesn't become irrelevant. It's a bit disheartening if the TM doesn't get to submerge due to never having a chance. Might be best to handle it as something they can do between missions, since then they won't be distracted.
Fifth Edition doesn't talk much about it because it will all be explained in Data Trails.
