The camshaft runs at half the speed of the crankshaft but that's still allot of rotations. I think I've seen 1000 miles as a typical break in cycle.
I've replaced 2. The first with OEM, which I stayed off the high cam for 1,000 miles. That one didn't last 7K. Replaced that one with hardened cam from Monkeywrench (along with oil temp/pressure gauge and 200 degree tstat) Same 1,000 break-in. So far, so good.
"If I've passed you on the RIGHT, you are in the WRONG lane!"