In my own testing several years ago, and later confirmed by other FitEyes members with tonometers who shared their findings, taking the prostaglandin-class eye drops at 8pm standard time (9pm daylight time) tends to give the lowest IOP over the entire 24 hour period.
I did extensive experiments where I took a prostaglandin-class eye drop (Xalatan) at different times of the day. I started in the early morning. After a couple weeks, I shifted two hours later. Like this I worked my way through the day until I was taking the drops at midnight. I was surprised to find that shifting the times did not predictably shift the peak efficacy time of the medication. I was also surprised that my overall daily average IOP changed with administration at different times of the day.
The change in time of administration did not just shift my IOP curve by that number of hours, it actually altered my high and low IOP values for the day (and hence the day's average IOP).
In my experience, the instruction to take prostaglandin-class eye drops "before bedtime" is too vague. For example, 9PM is definitely better than 11PM for me. As said, I get lower 24-hour average IOP from this change.
I also found the best time of administration to be relatively independent of bedtime. Of course, one could do even more extensive experiments than I did, but since my results aligned with what the manufacturers recommended, and they had done more experiments, I felt the question was answered. I have stuck with that time since.