Diary view options

Hi there,
Looking for a way to have 5 minute appointments but have text reminders set to give clients times at 15 minute intervals.
If I set the diary for 15 minutes it looks very cramped with 3 appts in there. How can we have a nice expanded 5 minute view but not have people receiving texts with a 9.05 time for example? The reason being that it is easier for people to work to 15 minute time slots when arranging their appts, even if actual contact time is less, and all 3 will rarely turn up at exactly the same time anyway so it is more of a guide – we just see to them as and when they arrive.
Hope that makes sense..
Any tips appreciated!
Thanks