Rogaine recommends applying twice daily but it does not say it needs to be every 12hrs. Does that mean I can apply it at 8pm then again at midnight and that would be just as effective as morning and night? Thanks in advance
Equally spread applications twice a day (every 12 hours) is better than an 8 and 16 hour schedule, but it is not practical for most people. I would try to space it out a little more than the 4 hour window you described. Usually it is applied when you get up and then again before you go to bed (just allow it to dry first).