Does DBCC SHRINKDATABASE free physical disk space during its run?
DBCC SHRINKDATABASE does not rollback when the process is killed so theoretically you'd be able to run it for a period of a time, kill the process, and have some reclaimed space (assuming there is any that can be reclaimed). See this for more information.
Also please see and research the warnings I provided against shrinking in my answer to your other StackExchange question.

...[it's] heavy operations, generally nonsensical to do because if
they grew to a certain size they'll likely grow back to that size soon
anyway and a growth operation is also heavy, and shrinking any
database files (except Temporary) does have a small risk of data
corruption.