I had jury duty about 2 years ago. We served for just over 2 days and, yes, I got paid by
UPS (8 hours/day) for my time away. It was a nice break from work but it taught me just how screwed up our justice system is. We spent 2 days listening to testimony and then spent 1/2 hour deliberating to return our verdict in a case that was a total waste of time for everyone involved, including the plaintiff and defendant.
I do know that you have to call in and, if you are not to report, then you must go to work. If you do go to jury duty and are sent home before your second shift starts I would think that you would need to call to see if you are to go to work. I would talk to your supervisor to see what he expects of you before your scheduled jury duty begins.