Seems to me than an endurance race with no time limit is a way of ensuring that "anyone can do it" - and therefore selling more places.
It's the equivalent of the London Marathon - any fool who hasn't trained can get round because even if you walk the whole way you will get your medal and then feel able to say "I've done a marathon".
I'm glad you said that and not me 
On the flip side of the coin it gets people off their arses even if they aren't going any faster than a walk. But yeah walking 26 miles isn't running a marathon.
To the OP, your times are fine, you can do it. Just train for it. 
What they said. If you're not podiuming, what's the point. If you don't think you can make top ten you're just wasting everyone's time. 
Doing triathlon/running/cycling just for fun is just immoral and wrong.
I'm fat, slow and ugly. I am 34 and didn't do any physical activity until my first child was born 3 years ago. I completed the Outlaw this year in 15h 55m, The Beaver in just shy of 7h, Wilmslow half mara in 2h 24m. I'm proud of my achievements this year. I'll never be at the pointy end and am not that bothered either, just happy i've found a physical activity I enjoy and is keeping me healthy.
What always amuses me about these speed peacocks is they forget that there is always someone faster than them out there. He walked it and got this, she run it and got this time, a semi-pro runner did it in this, the olympic champ did it at the WR time. Next year this WR time'll be smashed. What then is the race time that is classed as accceptable?
To answer your question, your training looks fine, take it easy on the day and most of all enjoy it.