My hospital will do them every 2 weeks but I also can't get appointments any sooner than 4-6 weeks. However, they have cancellations all the time so I always get in much sooner by checking daily for cancellation spots I can steal.
As for how much, it all depends on the fill #. For me:
#1: 3 cc
#2: 1.5 cc
#3: 1 cc
#4: 1 cc
I have a 10 cc band and I have my 5th one on Wednesday and I suspect they won't do a full one but we'll see.