Inspire by a lazy coworker, it means to come into work late, and leave early. For example, if the job you work at normally operates from 9 a.m. to 5 p.m., someone takes a Saber Day would come in at 10 a.m. and leave at 4.
"Dude, I think Jenny is leaving early today."
"Really? Didn't she come in late this morning?"
"Yeah, dude, she loves her Saber Days."