Me, personally, I would wait until Wednesday to start as they will take your weight on Wednesday as your start weight whereas if you started now you could have already lost a few lbs by the time Wednesday is here!
I just don't want you to possibly be disheartened the next time you weigh and you've only lost a lb when infact you could have lost a lot more... I hope I make sense lol!
I dunno though hun, there's no time like the present and all that though...