Specifically, what are you looking to do based on the system time?
I was considering an exercise/experiment/challenge to get stopwatch functionality with system timestamp variables. Save what system time it is whenever a trigger is fired that you might use to start and stop a stopwatch. Subtract smaller from larger and run expressions to convert & display as hh:mm:ss.
That'd be the time that's passed between two stamps. There might even be a way to make it work when you regret not having started a stopwatch at a specific time.
If that's feasible, it would serve as a workaround for this thing about MacroDroid resetting.
I understand that, by the way, and it makes sense. Just a bit surprised since my stopwatches show my neglect to, um, stop them.
On the oldest Android device I've got that I still put to regular use, I set up macros & stopwatches to time how long screen's off & on, charging & discharging. I just never got around to auto-resetting them or storing the lengths. My "screen off" timer now says over 1,893 hours and "discharge time" is over 2,021 hours.
If it's normal for MacroDroid to auto-reset from time to time, including stopwatches, I just wonder why mine tend to run so long. First guess is I should check the OS.