I have usually been able to get what I wanted within reason of the dates, sometimes a week or two before or after. Usually I am more concerned with leaving on a Fri for example, than which week it is. When they tell me that I can leave on a Sat night or Sun AM I would not accept that because I cannot take advantage of the weekend that I am not working.

Sometimes I have to call different airlines, fortunately I have miles in several of them, but usually in the end it all works out. I usually book several months in advance.

In booking SPG hotels, however, I have a 100% success rate for my first choice in dates!