AFAIK, wp_cron is not intended to create schedules with less than 1 hour recurrence, as it is no real cron.
see e.g. https://wordpress.stackexchange.com/questions/208135/how-to-run-a-function-every-5-minutes
btw., why would you want such a tight schedule ?
do you change calendar entrys evry 5 or 10 minutes ?
It is possible to create schedules with less than 1 hour, i changed an existing cron from 1 hour to 10 minutes. This cron imports the .ics files which were produced by your plugin to a calendar.
Yes, there can be changes every 10 minutes and same entry can have changes after 10 or 20 minutes.
ok, that’s correct, wp_cron also allows schedules with less than 1 hour, according to – the 1 hour minimal restrictions in the plugin is due to the use of the predefined values ‘daily’, ‘twicedaily’, ‘hourly’.
but as stated, I have stopped using / developing for WP long ago, so I won’t put anymore time in this IMHO rather exotic request.