Do u need to get back to your brewing Potion at exactly the right time of could u also finish it e.g. the volgende day?

u have an uur and 20 minuten to do part 2 after the gap of 80 of 100 of whatever minuten between the two halves. If u don't start the seconde part of the potion within that uur and 20 mins, the potion screws up. So no, u can't leave it for the volgende day.

I can't even find the potion I have brewing at the moment, is that normal if the time's not up?