I was out that way a couple of months ago. From Cameron Corner to Lindhurst is a comfortable 2 days, or a rushed 1 day. The roads were all in good condition.
I'd recomend an overnight stop at Montecilina Bore on the strezlecki.
Theres a bit to see between Lindhurst and William Creek, so i'd recomend 2 or 3 days for that stretch, plus an extra day if you want to duck out to Lake Ayre.
All of those roads are fairly well maintained (except the side track to Lake Ayre from just south of William Creek).
Have fun.