hi Cindy,
Emergencies are going to happen, so make sure to budget some funds for overtime. Also, check your state labor laws to see what is allowed.
Sometimes "floating" hours could be used. Full time employees could be paid for 40 hours but scheduled for 36. That way, if an emergency comes up, overtime doesn't always become a factor. My own hours are scheduled this way. Even though I rarely perform maintenance, I do get other "emergency" or after-hours calls, visits, tours right at lunch, non-stop days that require a trip to the bank after my work day, etc. If I have extra time at the end of my weekly schedule, there is always filing and organizing to catch up on (or for maintenance, inventory and prep work.)
We used to say "it all comes out in the wash," so working 35 hours one week and 45 the next was OK, because the market can be unpredictable. A few years ago the Bureau of Labor said that is not OK anymore.
So scheduling (and profit margins) had to be adjusted to reflect the new labor laws.
We also share our emergency pager. If the pager goes off, whoever is on duty responds to the call and determines if it is truly a maintenance emergency. Next, we offer the response to our part time staff. If a part time employee is unavailable, whoever is on call get's some overtime (like it or not).
Trust is important, but keeping records and verifying time spent will help too. If it takes four hours to take care of a half hour problem, investigate for sure!