What is it that you want to schedule? From an incoming call to an extension/call group? Or ?!?
Please give us more information.
In the Auto-Attendant, Call Handling, Custom Rules - you can specify a date or time, but the dates are non-recurring.

You would need to create 12 entries - one for each months 3rd Thursday.
In Canada we have a holiday in May that falls on the Monday before the 25th of the month called Victoria Day.
How can I schedule this day into the IVR to be accurate each year.
Similarly, we have a holiday that falls on the first Monday of August.
As is the case in the USA, fourth Thursday of November, we have Thankgiving as the second Monday of October.
Easter, as well, is a challenge.
On these dates I would send the IVR to our closed hours routine.