First timer for HIM- 18 weeks enough time?

my training for the last year has been primarily with weights; focusing more on figure-

it's been a few years since i was running marathons and doing any multi sport events. i'm training about 9-10 hrs a week right now.

All I know is that I did my first HIM this year in October.  I'd done many shorter races and had no idea how large a role nutrition would play in the race.  If you're reasonably fit and have a nutrition plan that works you'll make the cutoff times and probably finish.  But even if you're ultra-fit and don't have a nutrition plan in place, you could very well hit the wall and not finish.  A friend of mine did the same HIM as me as his first triathlon, he was an elite rower and an amazing athlete, but didn't realize how important nutrition on the bike was.  Instead of running in the 1:30's or so for the 13.1, he ended up running/walking around 2:30 because: 1. he pushed too hard on the bike, and 2. he didn't have a proper nutrition plan.

So anyway, if you plan on doing a HIM as your first tri, be sure you practice your nutrition plan during your training.  I can't stress that enough.  I also didn't practice it enough and paid for it about 6 miles into the run.