We were nervous about this drive as well -- started the Cassiar on 6/13/13, took our time, stopped a few places overnight, and got to Watson Lake on 3/18/13. 37, with its bumps and short gravel stretches, was actually in much better shape than some of the long gravel segments and other rough patches that we encountered on the Alaska Highway :)
Bridge delays at Bell2 bridge? Don't remember any, so must have been minimal. Bridge work over Liard River outside of Watson Lake did cause a delay as we had to wait several minutes for an oversized vehicle to be carefully maneuvered along the one open lane on the bridge. Not a long wait -- and rather entertaining to watch.
Relax -- enjoy -- it's a great drive and as others have said -- road is in great shape.