It is best to try and have some syns each day, as if you save them up for one big blow out your continuing bad habits, which isn't to say a one of big blowout is a bad thing but if its every week it may be bad for your losses.
I work my syns out for the week. 15 a day for 7 days is 105. Then each day I subtract what I used so if I used 20 on a Saturday instead of 15 it's not the end of the world.