Anyone one know how often the system runs for complimentary upgrades between T-24 and T-4?

T-23 for a SAN-DFW flight that I just SDCed to, and there's 7 seats open in F -- but not sure if it may still clear between now and T-4 (and I'm unable to check-in due to an error).

Thanks!

EDIT: Never mind, it just cleared a minute later after I posted this, so I guess it runs fairly often...