Plenty of time!

I would spend the off-season months working on your running and/or swimming, a couch to 5k plan sounds great. Then maybe start a sprint tri training plan 6-8 weeks or so before your race to bring everything together (OR just keep your mileage up in each thing, 2-3 times a week). Since the winter usually involves less riding anyway, this should work out okay.

Good luck! As long as you feel like you can swim, bike, and run those distances, you can make it.