If you start your birth control on the night of your ovulation day, does it still stop ovulation?

Probably not: You cannot count on a birth control pill stopping ovulation and preventing pregnancy until you have taken 7 pills in a row.

Not likely: Ovulation is a rather delicate/complex process that usually takes about 2 weeks from the start of the cycle to time of ovulation.. Regular use/timely use of ocp interferes with this process an thus prevents ovulation, but it is not likely to be effective if taking it only on the night/day of ovulation that is about to occur. The "morning-after pill" can stop pregnancy if needed. Consult doc.