Open the macOS Calendar application.
Each calendar at WebCal.Guru has a recommended update interval.
Unfortunately not all calendar applications honor this recommendation. In such cases the user must manually select the interval.
In the Info dialog, select the interval period under Auto-refresh.
For most calendars, Every week is good. Some calendars, such as Weather, update more frequently. For these calendars Every day is good.
Do NOT select an interval more frequent than Every day. Calendars are not generated more often than that, so updating more frequently will serve no purpose.
Finally, click OK.