byMonthDay

This term is proposed for full integration into Schema.org, pending implementation feedback and adoption from applications and websites.

Thing > Property > byMonthDay

Defines the day(s) of the month on which a recurring Event takes place. Specified as an Integer between 1-31.
Values expected to be one of these types
Integer
Used on these types
Schedule

Source

https://github.com/schemaorg/schemaorg/issues/1457