The question is, what's the real cost of that lost hour?
For starters, working out less could do a lot of harm to your improv game - it's possibly as devastating as nothing at all, but it might only be as bad as giving you a slight improvement. Improv is that kind of science where its hard to calculate how you're going. If you do more improv, the saying goes, you will improve and if you do more improv, you will get worse. Now don't expect to understand it or get your head around that.
Psychologically, there is also an impact. You walk out of the studio after two hours only slightly confused about how things are going but had you done the whole three hours, you'd be going home pretty sure that you were hopeless at it. When its two hours there is much more room for delusion as you think, "oh I probably wasn't that warmed up or something today," or "if only there was one more scene I'm pretty certain I would have finally found my groove."
Whatever the case, improv asks a lot of you and puts you in all sorts of situations and you are relieved of a lot of such situations by knocking off early. Situations frankly, that you're better off without. Over that lifetime, there'll be thousands of deadly viruses that you simply won't contract. Viruses that though killing you painfully and quite publicly, are considerate enough to be relatively quick and allow you time to say your last words. You'll avoid countless bad relationships, many with people of the wrong gender - or species - for you and frequently not even of your generation, some you didn't even know you were involved in to begin with! Not to mention the proctology and gynecological examinations you will be spared from having to undergo from unqualified and incompetent medical personnel, and you yourself will avoid needing to supply some of these very services to the afflicted. You avoid some sudden and spontaneous births, meteor strikes, police incidents, litigation, deliveries of inedible pizza and parties full of weirdos. On a physical level, you also get to avoid millions of slaps, kicks, punches, headbutts, stabs, knees to the nether region and shotgun blasts but you miss out on the sheer bliss of dishing these out to others.
You also, however, miss the chance to visit space and meet aliens, some of whom are pretty cool characters before you are inevitably forced to kill them. You miss out on some juicy church confessions with benevolent priests, which is a shame because an improv confession is just as legitimate as a church one and leaves you equally absolved of sin. You miss out on firing bad workers and playing shenanigans with senile neighbors. You miss talking animals, cartoon characters who have come to life and the opportunity to travel backward or forwards in time. And of course, road trips in cars with no doors.
You in short will go home a bit sooner to a simpler world that does at least make sense thanks to one less hour of improv. But you'll still wish you had that extra hour.