...Sorry Brianna... I missed your question about Stan and how long he can go without changing.
I used to know the answer to this without looking it up buuuuut, at the moment, I'm at a loss. Let's say, however, that it
has been quite a long time for Stan to be holding this form and as the Charon approaches, he'll be very close to 'running out of time'... Stan might appear to be "sweating profusely and otherwise showing signs of illness and/or fatigue"... He's not going to start "losing his shape" or melt into a pool of golden goo in the pod but it'll probably start to become apparent that something is ailing the engineering dweeb.
Update: Per Memory Alpha, a Changeling needs to revert to it's liquid form every 16 hours in order to rejuvinate... Sooo, that noted, since coming aboard the pod Stan has exceeded that limit by 2.25 times... We'll equivocate that to a human having been deprived of good, theraputic sleep, for three straight days, okay? Stan's exhausted, probably looks like crap despite having cleaned up and defunkified himself, and is likely becoming quite irritable.
Good question, by the by... especially considering that your Marines have been stuck with Mr Stinky for more hours straight than anyone aboard the Cerberus ever was.

Brianna and her leathernecks may do well to recall all of this during debriefing, huh?