pencil in event at increments

On my phones agenda, I can pencil in events at 5:05, 5:10, 5:15, 5:20 etc but not at 5:08.

How would you say the following?

My phone schedule agenda slots are in 5 minute increments.

How would you say , would you say on or in phone agenda and would you say 'pencil in'?
On my phones agenda, I can pencil in events at 5:05, 5:10, 5:15, 5:20

Is interval what you would use? How would you phrase?

I set the alarm ___ 5-minute intervals. I set it at 7:30,7:35, and 7:40 in case I don't wake up on/at/with the first alarm.

I set the alarm ____ 5-minute increments. I set it at 7:30,7:35, and 7:40 in case I don't wake up on/at/with the first alarm.

Thank you