is it possible to run a schedule script every 5 minutes? Currently I see on every 15 min as the closest interval. Any workarounds are appreciated

We worked around this issue by having multiple scheduled script executions.

How do you space them 5 minutes apart?

With multiple deployments and setting the start time 5 minutes later. There are several factors that control when the script gets executed, so I don't think there is a guarantee of a 5 minute interval.

The start time is a drop-down list with 30 min increments

This was done some time ago and I no longer have access to that environment. I have been unable to think of how this was accomplished. There must be something else that I have forgotten.