On our two HS days in January we actually did SDD, then Alien, then TSMM, then our FP+ at SDD. It worked great the first day, with a short wait at all. But on the second day we got to Alien just a few minutes later, and then TSMM a few minutes later due to that... and it was already a 30 minute wait. So only try to squeeze it in if a lower crowd day, and if you are one of the very first at RD. Otherwise Alien first is much safer.