I think you will find for the most part allot of the breeders plan specific crosses early on as those are the foals they plan to take to nationals, that way the foal is more so matured up nice come sept rather then just weaning and taking that chance of them possibly going through a rough weaning. If you look at nationals, all of the weanlings showing are Febuary/March babies.
Here in Ohio, it will be cold up until around March or so....so i've tried to plan my foals to arrive around April / May, atleast that is how it worked out this year. If you are down south, then having a January of Febuary baby you will probably be fine, i think foaling for the April / May / June is fine, i may leave a mare or two open next year so i can get her back on track for foaling earlier for the following breeding season.