Interrupt, sleep ATtIny85, lot of questions

OK, there's something that you could do in the interrupt service routine instead of nothing!

Set a flag to ignore the button until it has been seen to be released.

So all the wake up press woukd do is, well, wake it up.

There are several solutions. In general, you can always use program logic to decide if a button down condition is meaningful or shoukd be ignored.

a7