I use software with variable settings - i.e. every 300 hrs/3 months (which ever is first)
Getting the data into the system is a little trickier. There are systems out there that will let you know hours of use (normally they are also shockswitch/operator sign on off systems) if you have a large fleet or use these type of devices, the small (or no) cost difference is a no brainer.
If you don't do it that way then it's the hard way, find and record each piece of equipment
The third choice is to have the operators put the HM on their vehicle pre use inspection. The data is captured and then just pick a day to update the system every couple of weeks or so.