Swimming is such a small portion in terms of time of the race. An average to maybe a little above average finish is around 6 hours. Even if the swim took you an hour it still only represents 1/6 of the entire race. You can make up so much more time on the bike and run. Also swimming just isn't as taxing on the body particularly compared to the run. That is where your body breaks down.

There are a ton of training programs out there but i would say if you are putting in an hour or two a day training youll be fine. I did a 70.3 and just did crossfit and finished in just over 6 hours. Obviously not a great time but I basically rolled out of bed with just my crossfit training and was able to complete it.

The hard part for me was my body just not use to pounding on the pavement.