Thanks for the comments and advise!
I think I'm more concerned about the tool breaking than the bolt.

QUOTE: "... It's okay to pause long enough to catch your breath and unless you are in Triathlon training or equivalent you WILL have to catch your breath. Pausing to catch your breath is okay. Walking away from a head that is not completely finished in the torquing process is definitely NOT okay."

So what happens if the breaker bar tool breaks? Would it be okay to leave it for an hour or so while I hunt down another tool, as long as I don't lose my place? Or should I loosen all the bolts and start again when I get retooled if the bolts are still in spec (still within the acceptable length)? Is the head gasket ruined?