Q: I was wondering how to add additional time increment choices for the alert options in editing in the calendar. Thank you.
A: Unfortunately, there is no way to do this in the built-in iOS Calendar app.
As with other calendar features, the iOS Calendar application will support custom alert intervals set by other apps, but it will not allow you to set them to anything other than the provided options.
However, this means that you can set different alert intervals from other applications such as the OS X Calendars app—which will allow you to enter any arbitrary value when setting an alert—or third-party iOS apps.
If you’re syncing with a desktop calendar app via iCloud, iTunes or ActiveSync, this is probably the simplest—and cheapest—way to go about dealing with this, since you can set or modify the alert intervals there.
Doing this directly on your iOS device will require you to use a third-party app which you will likely need to purchase.
In looking at the Calendar app options in our own collection of iOS apps, a few that might do the trick for you include: Week Calendar ($2), which is designed primarily to display your calendar in a weekly layout, but provides the ability to enter custom alert intervals manually or customize the list of preset intervals. Calendars by Readdle ($7) provides tighter Google Calendar integration and allows custom alerts to be set at any five-minute interval.