It's hard, but it's not impossible. If you break it down by discipline, you have:
If the goal is simply to cross the finish line, it's actually quite 'easy'.
The harder part, certainly is the training to acclimate your body to the stress it'll feel on that day.
So let's answer some questions:
5-6 days is the recommended schedule. Typically a weekly schedule includes:
That could be a maximum of 10 workouts per week, and if you're doing 2 per day it could be 5 days. If you do what most do and stretch the long rides and runs onto their own days, it is easier then to run a 6 day per week schedule.
It's going to range from 10 to 20+ hours per week.
If you were to ask, 'how man hours per day should you train for an Ironman?', well that answer is going to be 2-6 depending on number of workouts that day, and the length.
Our Ironman training plan tops out around 19 hours in a peak week. That breaks down like this:
The above is an example of one of the longest weeks in the plan. The first few weeks would be an hour or less per session and you'd build up over time.
But in those 4-6 weeks of really peak training, it really does become like a part time job.
The short answer is, it's as hard as your training allows it to be.
If you execute a solid Ironman training plan, even one designed for beginners like this one, you'll be in good shape come race day.
You can get away with significantly less if the goal is to finish in 16:59, but you run the risk if injury.
You can also train quite a bit more if you're able, but again, injury and 'time' come into play.
Ultimately, find a plan that fits your LIFE, and if you do the work - finishing won't be all that hard!