Hi Steve,
Yes it is.
You start the synchronization at the bottom of the Import/Export section of the Admin interface.
If you check the -Run automatic sync- checkbox the synchronization is repeated at regular intervals.
Before starting you need to set the -List of external upload links- and the -Schedule recurrance- in the Settings page.
Two remarks:
1. The automatic sync relies on a WordPress mechanism to schedule jobs. This mechanism only runs when the site is visited. When the site is not visited for a day the job does not run even if it is set at an hourly interval.
2. The iCal (ics file) format includes an UID (unique identifier) to identify an appointment (booking) uniquely over the different calendars. So in a sequential download appointments already present can be skipped or updated. Unfortunately some external calendars do not comply to this standard. Each time a download requested from such an external calendar generates a new different UID for the same appointment which result in multiple records with the same appointment. A workaround is first to delete all appointments before downloading the external calendar. For these external calendars the possible recurrent schedule of the download is not very useful.
AirB&B is one of the sites with this problem.
Regards,
Jan