What day of the week should I tip my hotel cleaning staff?

If I'm staying in a hotel for a week, and if I only tip one day, which day would be best to ensure that the cleaning staff that clean my room the most actually get the money I leave?

i dont know why but i think thursday...really i dont know why it just seems like a good day for it! lol

i often hand the tip dirrectly to the maid onve i'm sure of who das and will be cleaning my area http://answers.yahoo.com/question/accuse_write?qid=20070823192731AAY0Vel&kid=Q5lZL3PCUFmmAOv0qf9n&s=comm&date=2007-08-24+11%3A34%3A02&.crumb=