For you equipment, try oil samples. It is a great and inexpensive too for setting a maint. schedule. When you change the oil, fill the sample cup and mail it in. In a couple of weeks, you will get a sheet that will list all metals involved with the engine and % of each found in the oil. It will also tell you what % of oil life was left. If you have a certain metal % that is too high, it is indicating that you have a problem that you can fix before it goes down in the field. The manufacturers schedules are standard. Each operators situation and use of that machine is different. This is an inexpensive way to custom tailor a maint. schedule for your biz.
The kits are available for under $20. The info. is priceless.
As far as a dedicated schedule. I leave it the responsibility of a single person. I do it personally, but as I grow, I will pass this on to one person alone. One person keeping tabs on this makes it easier. It only takes a few minutes of an evenig to change the oil and filter. You should grease daily anyway.
Take care of your equipment and it will take care of you!
Morgan Lawn Care
"Committed to Excellence"