I think that is about right, John. The whole way, if you bike Rob Brook Rd and bike/push by Birch hill, then dump the bike and hike is about 2 hrs at a semi leisurely pace, slightly faster if you don't mind the river ford and come in directly from the Kanc. A few weeks ago, hiking in all the way at an easy pace via Rob Brook, it was about 2:15-30. I have had it take as much as 4 hours getting in, but that was with a ridiculously big pack and trudging like a snail. Cruising out, I can make it in about an hour with the bike.
I've got the latest version of directions and maps on mountainproject if the ones here are not clear enough. The key is to get a good early start while it is cool. I am planning on the end of this week, but I bet the bugs will be hideous now for a while, especially along Birch Hill.