The Belknap Range is in my backyard, and I have traversed its 12 peaks a handful of times. My times have generally been around 4 hours, trailhead-to-last-peak. On July 17, 2015, I set a new PR of 3:50, beginning at Durrell Mountain Road and ending on the summit of Mt. Major. I then descended to the Mt. Major parking lot for a trailhead-to-trailhead time of 4:09. From there, I jogged and hiked back to my car on snowmobile trails and roads, around the southern end of the range.
Here is a link to the GPS data: connect.garmin.com/modern/activity/838609633
The first split is the time from Durrell Mountain Road to the summit of Mt. Major. The second split is from the summit of Mt. Major to the Mt. Major parking lot. The final split is from the Mt. Major parking lot back to my car on Durrell Mountain Road.