I believe some of this was touched on here backgrounder.extra_timeout_in_seconds vs backgrounder.querylimit but Justin Mangue may have more details as well. I wouldn't think that a backgrounder going for more than a few hours would be advisable though.
Just to close the thread.
Had contacted the Tableau Support team and they informed that there is no limit on the Maximum limit on the Backgrounder query run.
But it is better not to run the backgrounder for long time