You might want to rethink that, because I loaded up an invite-only lobby just to record more footage of this glitch in action, did absolutely nothing for 23ish minutes while I ate breakfast, and the IGT was running in the background. Recommend switching to RTA for co-op runs if the IGT on PC operates consistently with console.
The in game timer counts in real time, and pauses during Zed Time, and yes, the in game timer continues to tick during Trader time, so you'll have to take that into account, just like the rest of us.
While we're on the topic of the in-game timer though, there is one oddity about it I want to address that I'm surprised hasn't arisen already. I don't know if this is the case on PC, but on the PS4, I've noticed that when playing co-op with a friend, the timer actually starts counting up in the lobby menu, before the match even starts. We took a 40-50 minute lunch break in the lobby menu after a match, and after we came back and readied up, the timer had already ticked 40+ minutes.
Normal - Short
So, here's a clip from the end of a run I just did on Santa's Workshop. Was experimenting with some multi-class strats, got boned at the end of wave 4 with 8 leftover Zeds on a 6:40 pace, then on Krampus, while fighting him, he glitched out and killed himself. Link is below.
Haven't uploaded the full run cuz I want to hold off on a submission until I get a ruling on this. I've had something similar to this happen on a Hostile Grounds run too, only difference is he didn't kill himself this time. Link below.
I think what could be done for endless is to have certain round milestones as categories, like fastest round 10, 25, 50, 100, etc... like COD Zombies does their round charts, though the longer videos for higher rounds would be a bit of a hassle. For example, I'm doing a high round on Spillway, (paused on round 165 at the time of writing this) and my time at the start of round 51 was 1:15:11, or 75:11 as the in game time would display it. It would be the same rules as a regular Survival game for the most part, just applied to Endless, with the end being when the boss on whatever milestone round is killed. This is arguably my favorite mode in the game, and I would love for there to be competition for it in some form here on the site.