Can I change the time increment from 15 minutes to something else?
Sure. If you just want to make the change just for you during your current session (until you close the file) select the "Settings" tab in the calendar sidebar. Then change the "Time Scale" by selecting a new number in the drop down.
If you would like to make a permanent change that will affect the default setting of all users edit the script "Load Calendar Settings - On Startup --- Edit Configuration Here ---". Find the comment labeled "What should the default time increment be in schedule views? (Default is "00:15:00")" and edit the variable below called "$$sc_TimeIncrement" to your new value. Keep in mind that these times are 24 hour times and do require a format of "00:00:00".
How can I see more all-day events at the top of the screen?
Views that show time scales (like the Day and Week Schedules) show all day events at the top of the screen in a separate section. The calendar shows 9 such events by default. If you'd like to see more you can change this setting in the "Load Calendar Settings - On Startup --- Edit Configuration Here ---" script. Just edit that script and find the comment labeled "What is the maximum number of all day events to show on the Schedule views?". Then change the variable below it "$$sc_MaximumNumberAllDayEventsToShow" to another numeric value.
Note that you'll have to run the "Upon Opening" script to see these changes take effect.