I can say from experience that staying up late works for a while, but you'll eventually hit a wall and hate life. Now, if I have a side gig, I go to sleep almost as soon as my son is in bed (I say almost because you need to have some non-parent time). Then I wake up early, like 4am early. The benefit is you're fresh and hopefully have 2-3 hours before your oldest wakes up.

Of course when the baby arrives you can forget side gigs for about three months because it'll be madness. However it's only three months or so of crazyness, and they're only that small once so enjoy it! :)