From GGB to GGB, about 6 hours, maybe a little less, going at a social pace (i.e., stops to regroup, refuel, etc.) and doing the route I had in mind, which you can see here. The route is a little inexact provides a general picture -- about 55 miles and 5400 feet of climbing (that sounds a little high to me...)

If you can't do the whole ride, there are places you could shorten. Here they are, fastest/shortest option first:

1) Ride with us up Railroad Grade to West Point Inn, then turn left on Old Stage Road (which is a gravel fireroad, then a paved path.) Old Stage eventually takes you to Pantoll Ranger Station, where you can then take Panoramic/Highway One back to Sausalito.

2) Ride with us all the way up Railroad Grade to the top of Tam, then from there take roads (East Ridgecrest/Pantoll/Panoramic/Highway One) back to Sausalito. (We'd also be taking the road for part of this way, but then splitting off on a trailhead before reaching the Rock Springs parking lot.)

3) Ride with us to the top of Tam, then on Rock Springs/Laurel Glen Fireroads, but then when we reach Ridgecrest in the middle of the Seven Sisters, head south (and ultimately back to Pantoll) instead of north toward Alpine Dam (which is the way you'd go if you were doing the complete route.)