[Plugin: All-in-One Event Calendar] More frequent ICS Import auto-refresh

The list of Auto-refresh frequencies are the ones that WordPress supports. We can look into adding extending WordPress to support more frequencies.
There are a few possible reasons why ICS import is slow:
1. Connection between your server and the server where ICS is located is slow.
2. The events in ICS file have recurrence rules that require a lot of parsing – eg 1 event that repeats everyday forever – We have to create 365 entries in the database just for that event and if your server doesn’t have a lot of cpu power and ram it will add to the loading time. Imagine if you have 10 events that repeat daily forever, that’s why we always advice users to set an end date for their events.