Better re-read my earlier reply. 1.5 days to Denver = zen time for me. I like that sort of riding.
Accordingly, if I did book all 5 weeks between May and September I could probably extend the timeline on this sort of trip to 2 weeks, so 12-15 days.
Realistically, flying out and then back to and from Cali/Vegas plus renting a bike there could easily take two full days. Considering that it is possible to get to and from Denver / Sturgis in about 1-1.5 days, the math doesn't look so bad. The difference between flying there or riding all the way is only about a day, with the advantage of riding your own bike and saving a couple of grands.
So far I've been out there six times and all trips except one where on my own wheels. This works for me because I consider all riding west of Denver / Rapid City as part of the road trip as opposed to the part of "getting there". Of course, if the only goal would be to ride the PCH, would have to reconsider.
As for the available time, if California is the ultimate destination, scheduling a two week trip is definitely a better idea. There are just so many amazing roads and places in the south-west, with such a variety of landscapes. It would be a shame to miss some of those out due to lack of time.
And a final note about tent camping, in most of Utah, Arizona and Cali, is not really feasible in July/August as it is too hot. In those areas I prefer a cool motel room. We do take the camping gear with us for backup and for those places where it is too difficult to find a room (like Yellowstone). But if we have a choice, we either stay at motels or rent KOA cabins, which is our preferred option in cooler places.