Yes there is. But it's just a lot easier to say random because the equation works out to be exactly 50% to 50%.
NOTE: 3 published official guides, including Nintendo's only creation, said "day and night." No that is not true. It depends on a mixture of a few numbers: nature decision number, gender value divider, and personality value. These 3 numbers' calculations are so complicated, yet comes to something that you can simply round to 50% (something like 49.97 or something, and 50.03 the other... oh i don't remember but it's something really close) for both.
Time is not related, because you can trade a wurmple to FRLG which doesn't have the time system, and it will still evolve (at the same time, it means that Eevee will not result in Umbreon or Espeon, and that the time-dependent healing moves all heal 1/2 of max hp just like the stadiums)