They will, with permission, let you check your hull out in the company of one of their personnel.
I usually go about 12 months, but as some of the Regatta goers will attest, this is a little longer than I should go. It all depends on how much you use it, and where you're moored. Careel Bay is pretty clean, but no one there goes more than about 14 months. Gladesville, where we used to be moored was much less time between slips.
For me, it's much quicker and easier to have someone else do the work. It's really hard for me to get a weekend totally free, and there are few places left in Pittwater that will rent you a slip and stand for very long. When I retire of course, I'll be doing it all myself

Michael