No matter how good we are, there are always going to be crunch periods. These are often structured around date-specific things where we want to look our best: demos, release dates, big new client starting, etc. We work really hard, pull some late nights, work a few weekends, and often something really great comes out of it.
It's really tempting to take the next day off. After all, when you've worked the last few weekends there's a big pile of laundry needing to be done (and a serious sock shortage!). As a manager, you want to give your team a reward for all the hard work, and a day off is usually appreciated.
Don't do it.
You've got to run all the way through the finish line. (I think this is a track and field term, obviously.)
After all, your big day - demo day or whatever - is just the start of your users' big days. They're going to need support. Maybe it's questions, maybe it's bugs, maybe it's congratulations. Either way, you need the team around for that. You need to make sure that all your efforts are still showing themselves as people start to use your system.
So don't take the day after the demo off. Take a day off a week later, or two weeks later. Once you've made sure you ran all the way through the finish line, then - and only then - you can stop running and take the time off.