How long does Rubeola titer takes to come up after the MMR booster?

My school requires me to show immunization to Rubeola through a titer to be enrolled. I had the titer done, and it came back negative (no numerical value provided, only that it was less than the range). I had the MMR when I was young, and my titer for Rubella/mumps are good. I had the MMR Booster, how long does it take for my titer to come up?