Do you do long rides on your bike? Are you used to having to dig deep to finish long rides, etc?
If so, personally, I reckon you’ll nail 2 hours. I’m not a runner really but I decided a while ago to do a half marthon and with very little in the way of training (and by that I mean, none) I did a 1:45.
The only way I was able to plough on was that I’ve done a bunch of 24 hour solo races, a load of 12 hour races, 105 mile sportives and assorted long rides.
If you’re used to doing this sort of stuff to your body then you know how to grit your teeth and get on with it, plus I think mentally two hours is no real issue if you’re used to riding for 8+. Especially if you consider that your cycling fitness alone will probably get you to beyond an hour without too much effort.
If you just went out and ran 6miles with no prior training then you’re obviously pretty fit already, give it a go, I bet you suprise yourself and your running buddy.