Send caller with scheduled appointment directly to specified number when they call within 15 minutes or X minutes/hours of their appointment time. The?

Send caller with scheduled appointment directly to specified number when they call within 15 minutes or X minutes/hours of their appointment time. They are calling for directions, to reschedule/cancel or confirm. They might as well reach the right person right away. But I like to send most other calls to voicemail at other times. Same person calls at 12am the day before = voicemail. Still want the phone system to send others the link.