I applied in this Feb. and got interview in Apr., so believe u still have time to arrange ur application--
1, submit ur complete application materials first to try for an interview, and send ur GMAT report to UST later; if UST feel u're qualified in the interview, they would give u a conditional offer; and after they receive the official score report, then will transfer the conditional one to an official one;
2, if u really have no enough time to prepare the application materials before taking GMAT, just make sure u will get a reasonable score (no need so high), and try to grasp the last round application!
BTW, contact and communicate with ur recommendator in advance, make sure they can provide sound support to u!