Monday and a day off

I need to combine two things this week that don't go together well. 1.
A week of less exercise in order to perform well on Sundays 10km and;
2. The additional milage I need to get under my belt for the half
marathon in less than 3 weeks.
Today is a rest day but I am really worried that the half marathon
will suffer. My max so far is 10km and it's a bit of a big jump to
21km so my concern is still that I won't make the distance. I am still
carrying a stone to much in weight and can't find the time to do the
extra milage.
How do people find time do do training for longer distances such as
the Ironman etc? A friend of mine who has no wife and kids and did one
last year said that he was training in excess of 20 hours per week.
How do you honestly fit this in? I am already getting up at 4 to 4:30
every day so I cannot get up earlier for a run! People that do these
long distances must make huge sacrafices in order to manage them and
my hat well and truly goes off to them.

I am in awe...