Everything is going to change in August. Currently if you take the written you have a 24 month window to pass the checkride. After August you have to complete an ATP training program to take the written for a ME ATP. In the regs it says even if you hold a non ME ATP, you will have to go through the training program to add the ME ATP. So if you're ever going to want the ME ATP do it now before your pre August written expires in 24 months.