EXCLUSIVE

Steve-O is a free man ... getting sprung from an L.A. jail after just a few hours.

The "Jackass" star turned himself in Wednesday night and was sentenced to spend 30 days in lock-up -- but barely had enough time to get comfortable ... due to overcrowding.

Steve was in his cell for a mere 9 hours since L.A. County jails are overcrowded ... non-violent offenders almost NEVER serve their full sentence.

TMZ broke the story ... Steve-O got jail time after climbing a crane in Hollywood for an anti-SeaWorld stunt. He pled no contest to trespassing and possessing fireworks.

Tilikum would be proud.