Do you notice any gains being less during that time?
sleep is just one factor involved.
progress is SLOW whether one has 3-4 hrs of sleep or 8-10 hrs a night. I find it's better to keep working out during my busy season than it is to take time off. do I make gains, during that time? No, but I do maintain what I have much better if I continue to workout.
if you have one night you didn't sleep much, play it by ear. if you are tired during the day, maybe skip the gym that day. if feeling up to it go.
there isn't some yes or no answer when it comes to training. consistency in everything you do is what pays off over the yrs. consistency with diet, consistency with training, consistency with sleep, consistency with schedule... so if you have one day out of the week or month that something hits you unexpectedly it isn't going to adversely damage your progress over the long term