Can I change the time increment from 15 minutes to something else?
Yes, individual users can change this on the fly on the "Settings" tab in the calendar's left-hand sidebar.
Administrators can change the default time scale for all users in Admin Settings / Time Scales.
How can I see more all-day events at the top of the screen?
Users can't change this on the fly, but as an administrator you can decide on the maximum number of all-day events you'll show before showing "X more" and forcing users to switch to one of the list views. You'll find this setting in Admin Settings / Views as "Maximum all day rows to show".