You're better off just waiting until July, which is just less than 90 days away anyway. Meanwhile you can use the METV to enjoy your time in Thailand until July, leave, then apply for the DTV.
I now do this calculation myself every time before arriving. 180 days from Friday March 7 = September 3. So expect your stamp to say either 2 Sept or 3 Sept. A difference of one or two days isn't a big deal so I wouldn't fuss over it. Plus, they may have a different way of counting that 180.