Specifically replying to Ron here...
I think i originally misread your post... but if this is wrong too, ignore me haha.
If you want something to run every 5 minutes between 8:30am and 10:50am, do a Custom time trigger instead of an Interval trigger.
Create multiple triggers that don't overlap.
1. Select Every Year, Every Month, Every day, just the hours of 8, 9, and 10, and for this first one, just the 30,35,40,45, and 50 minutes of the hour, 0 seconds.
2. Select the same as above, but when it comes to minutes, select only the hours of 9 and 10 (not 😎. Select minutes 0, 5, 10, 15, 20, 25
3. Same as above, but only select 8 and 9 for the hour, and 55 for the minute.
That'd get you every 5 minutes between 8:30 and 10:50am if i'm not mistaken ;-)
Brian