I didn't mix the chemicals up yet, i mix them the night before (with the exeption of rodinal, which i use right away) and then use them next day. i reuse microphen stock 10 times and it keeps for over a month in a tightly capped nearly full bottle (and add 30 seconds each time; i do not reuse stock if the roll is a "once in a lifetime" or critical, i just use fresh chemistry), it preforms outstanding.
Come to think of it, given that a couple of people on here have mentioned that it should be okay i will use microphen rather than D76 merely because i am familliar with it, so i will mix up some fresh stock ready tonight... seeing as the powder is a pain to dissolve! i don't pre-soak either.