Depends
It largely depends on time of year and of course during holiday weeks.
I have found that moorings start to empty out mostly on Sunday,Monday,and the rest of the middle of week and they start getting crowded close to weekend,if going to arrive on a Thursday you should get there really early in the morning,best times are the early part of the week.
All the trips that I have made to block I have anchored,one year I got there on a Thursday and all moorings were full and anchoring was very crowded.
Nick