Ok, your doing a long ester say test e and you want to switch over to test prop at week 7 that's fine because prop will kick in straight away and you will still have test e a long ester in your bold stream for a few weeks do you get me? Now switch over from short ester to long ester is the problem because under a week that short ester is going to be out of your body and the long ester will take 3-4 weeks to kick in. So you will have to kick start the test when switching from short to long.