On summer days and typical clear sky winter days, it takes about 30 min to go from Fallowfield to Tunney's pasture station (route 95). From Fallowfield to Hurdman is about 45 minutes (for 95). Express bus saves you about 5-10 min of commute generally speaking, compared to taking local bus then transferring to 95. Many people choose express because they do not need to transfer to another bus, and also because finding a seat on 95 can be difficult.
You can definitely expect delays on wintry days, particularly the morning after a snowy night. Sometime your express bus is stuck in Barrhaven for 30 min because the city did not clear the snow in time. But this happens rarely generally, and I am sure that Kanata and Orleans face the same problem. You can avoid this situation by either driving to Park&Ride or take buses that do not go on the major roadway like Woodroffe. Buses like 71, 76 are to be avoided. 73, 77 are ok, because they go on less busy Fallowfield Rd, or turn away from Woodroffe early. Starting from Fallowfield, the commute to downtown is pretty smooth. The intersection around Lebraton Station can be quite busy sometimes.