Hi, first off congratulations on signing up for what I think is probably one of the best first time tri's you can do. Not only is the venue and course perfect, but xtramile know how to put on a race and that course has been run for years now. Disclosure, before moving to NZ then I referreed that race 3 times I think, and either crewed, refereed or worked for them at another 20 or so of their events.
Your first one is all about getting to that finish. So do what you want to be comfortable. It's an earlyish season one, so it could well be nippy in teh morning, and unless you've come from a swim background then you're likely to be seeding yourself to get an earlyish swim time (hence even colder). So 30 seconds to towel off isn't a big issue.
But as a serious point, then have a shower at home then try to put your kit on. You'll find that your cycling jersey will stick and be really hard to put on. The trick is to put the jersey on before you start the race, then roll it up as you take it off, leaving it rollled in a hoop, so that when you put it on in the race then it sticks and just unrolls.
Turn up early, don't be flustered. Dont swim too fast, there's still the bike and run. When you've swum way too fast, then don't try to carry on pushing on the bike and hoping that the run wil be ok. When you get back from the bike totally knackered as you've swum too fast and then biked too fast, then bollox to it and just head out on the run and pray 
