Overdue notice triggers are still in days only, so it is not possible to notify patrons as soon as an item out is due.
In the meantime we are using the patron_emailer_pl functionality to send 'late' notices for hourly loans. For example when a laptop loaned for 5 hours goes late, the email is sent within a few minutes. OK it means running the emailer script often: */5 * * * * /usr/share/koha/bin/cronjobs/patron_emailer.pl --report 974 --notice ODUE_LAPTOP --module circulation --commit Better than nothing, I suppose.