jobStartDate

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

Thing > Property > jobStartDate

The date on which a successful applicant for this job would be expected to start work. Choose a specific date in the future or use the jobImmediateStart property to indicate the position is to be filled as soon as possible.
Values expected to be one of these types
Date
Text
Used on these types
JobPosting

Source

https://github.com/schemaorg/schemaorg/issues/2244