Can a county jail run by a sheriffs department keep an arrested person in jail for as long as they want? What if they refuse to release them?

No. Open ended sentences are illegal. You can sue $900/day for each day over what the sheriff said OR a court rules reasonable by case law , precedent, or rules of court.. Whichever is more days.

I am assuming here they are not simply being held before hearing due to not meeting bail? A reasonable few days until grand jury or hearing is acceptable. Not an actual sentence that is arbitrary or exceeded, or simply that it takes 1-24 hours to process someone out. I had to wait until next morning for video court as a dumb judge had warrant out "for my arrest". I had paid the fine, he was Not "computer literate".

have they been arraigned ? time for a lawyer .

no, of course not