Speeding up Google Calendar .ics Subscription Refreshes

My project of the moment preventing me from going to bed: configuring a Google Calendar script to work, such that it will force GCal to refresh its .ics subscriptions from Fastmail every 15 minutes, rather than the default 12-24 hours. All so then SkedPal can read GCal and have accurate and timely data from which to build my daily task schedule. Why can’t SkedPal simply support standard CalDAV?