I have a gargage heater with a mechanical timer limit switch dial that has markings on it and three slides to set on time ,run time Where should these slides be set marks indicate 5 - 100 and should I spray this with lube?

If it is mechanical timer you just set it to the number of minutes you want it to run. Set on 30 for 30 minutes run time.

Someone got smart and put a timer on it so they would not forget to turn it off. Good idea.