How strict are you on bedtime?

LO is almost 4 months old and we are finally in a somewhat good routine (yay!!) last feed is at 7:30, bedtime at 8:00. This happens almost every night. If, on the occasional Friday night the hubby and I wanted to hit up a brewery with the little guy, do you think we’d be throwing him off with a 9:00 bedtime instead every once in a while?? Don’t want to mess him up currently so we have been sticking to the schedule! But wondering if anyone had success with a flexible bedtime every once in a while. Thanks!!