How long can you grind?

Forever if its with a hot girl.
Actually grinding is really repeititive for me, so like 2 hours?

I knew I wasn't the only one who did a double-take when I read the thread title.

Anyyyywaysssssss. Longest I ever did was... 10 hours, my brain can't handle more than 8 on a regular basis though, my eyes hurt like a peach.

 Spoiler

It feels like someone is raping my brain, like.. in one ear and out the other.

I usually do 4 hour intervals, or just 4 hours at once. I get bored easily, so unless I have something like Anime or Porn playing on my screen while I train, I stop like.. every 30 min.