Take your paternity leave (as much as you can). Drop down to a four day work week, even if you feel like it's a risky question to ask, as soon as you can.
Everyone will tell you that you can't get the time with your kids back - and they're right, so spend the time with them now.
Can't echo this enough. You cannot get the time back. Tomorrow is never the same as today.
I have no regrets, but I do wish I hadn't put off anything to do with my daughter's childhood. There is no "later" when you say "we'll do this later". Whatever it may be, do it now or you might never get to do it.
Everyone will tell you that you can't get the time with your kids back - and they're right, so spend the time with them now.