@Kyle B,
The key to calculating probability correctly is always the same, though the exact method will differ:
(1) Figure out the total number of ways an event can occur
(2) Figure out the total number of ways the desired event can occur
(3) Divide (1) into (2) to get the probability.
There are 60 x 24 = 1440 minutes in a standard day. There are 365 calendar days in a standard year. So the answer to (1) is 1440 x 365 = 525,600.
There are two times in each day (a.m.and p.m.) for the desired event to occur, so the answer to (2) is 365 x 2 = 730.
If we invert the division for the sake of clarity, then the answer to (3) is 525,600 / 730 = 720 to 1 odds.
This ignores Daylight Savings Time, leap years, leap seconds, and other irregularities. It also assumes, without reference to birth data, that all times of day and all days of the year are equally statistically likely for births.