Hi stevenrealife,
Welcome to Apple Support Communities!
We see that you are having an issue with setting up an appointment in 5 minute increments. We want to help. You should be able to make an appointment to the minute level, for example, Doctor appointment at 9:52 a.m. To make sure that we are covering everything, here's how to Create and edit events in Calendar on iPhone - Apple Support.
If you are not able to do that, have you tried restarting and checking again? That would be a good next step.
Reach back out with any questions or if you have a different issue.
Best Regards!