Arming distance is the distance from lauch that the warhead arms. This is a safety measure designed to protect the firer from blowing himself up by engaging targets too close. It can be done by several methods, all of which pretty much do the same thing in the end, arm the warhead at a preset distance. That distance may be at the muzzle, it just depends on the weapon. That range is refered to minimum range.
There's also what's called minimum range on guided weapons. Guided weapons, like the TOW, take a little time to aquire both target and missle and make correctional guidance. So these weapons won't work below a certain range because they just aren't being guided until they get far enough out. The range varies with the weapon as well. Examples are as short as 25 meters (Milan) or as far as 1250 meters (Shillelagh) and all ranges between. It just depends on the system.
I looked in several references I have laying around, and all of them had minimum range as "point blank". They probably all got it from the same source. I left the Army before they started using the "Carly G" (it replaced the M67 90mm in the Ranger BNs) and since it was a Ranger thing anyway, I wouldn't have seen anything specific on it. Flight time to 700M is something like 2 seconds, so figure it arms pretty close in. There's a booster motor that ignites a few meters from the muzzle, and my guess would be that also arms it. That's just a guess though, with no basis in fact. I don't know where you'd find a manual. I'm sure they're out there though, as everything is.
Ross