So, at least 30 seconds, I guess?
As said, rather make it configurable. This is a real-world system… 😄
When I was starting to use subscribed calendars, the most obvious starting point was to add the calendar to the Google calendar attached to my Android phone.
The first problem I encountered was that Google Calendar does not support HTTP-Auth for calendar subscriptions (see https://webapps.stackexchange.com/questions/2018/accessing-a-password-protected-icalendar-feed-from-google-calendar and https://productforums.google.com/forum/#!msg/calendar/vjSZRkJHaWA/36jXqGb5puYJ).
The issue I found was that there is no concrete SLA for subscribed calendar updates: https://webapps.stackexchange.com/questions/6313/how-often-does-google-calendar-update-its-other-calendar-feeds
My suggestion is that the information for ICSx⁵ (eg https://icsx5.bitfire.at/) could do more to emphasise these differentiators: support for HTTP-Auth, and control over update schedule.
Thanks for the suggestion!
Would you mind sending a merge request? https://gitlab.com/bitfireAT/icsx5-website/