We started in Seattle on May 25th and were in Minneapolis around mid July (I remember being in eastern ND on July 4th), including rest days. However...
1. We took the "long" option through MN. There is a shorter option included on the map.
2. We did some short days along the way when we could have done longer yet still manageable days.
3. We followed the route into Canada, staying in Waterton Village and McGrath before heading to Cut Bank, MT. You can probably trim two days by heading directly from St. Mary, MT to Cut Bank.
4. We took at least six rest days in that stretch. Two were probably not really necessary, but we had to take the group's varying abilities into account. Plus, we had a 93 days schedule for the entire trip, which is on the long end.
Sometimes the WA par of the route leaves you few options unless you can do a lof of miles and climbs. After the Cascades crossing, where the natural overnight is in Winthrop (bike-friendly KOA), you'd have a long day (109 miles) if you tried to do Loup Loup and Wacunda Passes the following day. Instead you will likely do Loup Loup, overnight in Tonakset and then do Wacunda.. Maybe you could make it from Tonasket to Colville (93 miles) over Wacunda and Sherman Passes in one day, skipping to town of Republic in between, but it’s not something I would want to do unless really pressed for time, but that’s because I tend to be a one and done person when it comes to long climbs. Your mileage may vary. Once you get onto the “High Line” (east of Cut Bank, MT), you have more options. It’s relatively flat in most places, and you can get some killer tailwinds. We did two 45 mile days that could have easily been made into one day for these reasons. At one point I was cruising along at 28 mph and actually sustained 32.5 mph for about 4 miles.