This is my personal opinion, and not a stated fact, but I have come to believe that the WL matchmaking system is based on matching people with the same number of current wins, rather than base on a win/loss ratio. Given this, if you are struggling to move up the ranks in WL, you are better off playing your games later in the weekend rather than earlier. This is because if you have, say, 4, wins currently, you would rather be matched up against someone whose current record is 4-8 rather than someone that's 4-0. You will increase your odds of playing someone with the same or similar number of wins and more losses later on in the weekend rather than earlier.
Again, this is just my opinion on match-making, but it has been borne out through trial and error. I find that I have a better result if I weigh my games more heavily toward the end of the week. Take this however you like!