I haven't been getting much OT lately, but when I get it, it's always in 8 hour chunks. The first week I got permanent promotion, I put in 7 sixteen hour days & then worked my regular 8 hour shifts for a few weeks without a day off.
I do work a crazy rotating schedule. It starts on a Tuesday, day-shift 6am to 2 pm for 7 days, 3 days off, then 7 days patrol- shift 5am to 1 pm, 4 days off. Then comes swing-shift, 7 on, 3 off, & tonight I started graveyard. I get off shift next Thursday morning & start all over the following Tuesday.
I can't imagine staring at a screen for 13 hours, unless I'm playing a MMO.