If I switch the CH to TWICE and the hot water to ONCE, then the hot
water is on from ON1 (7am) until OFF2 (10pm)
not ON1 and OFF1 !

Yes, this is a very useful feature. It basically allows you to set morning
and evening times, but fill in the middle on weekends or when you take a
sickie. It is very standard for programmers to work this way.

Why do you want to control the hot water independently? I normally stick
mine on 24/7. Modern insulation standards mean that you won't waste much
energy doing so. Also, if you have a gravity hot water heating circuit,
you'll be unable to turn off the hot water when there is a call for heat
from the heating circuit anyway. (You'll also get pitiful reheat performance
by modern standards).

P.S. the model you have looks identical to the one I've got on my old system
(shortly to be RIP, hooray!) However, mine seems to have a mind of its own
and doesn't seem to come on when instructed. Horrible thing. It is
particularly annoying setting the clock. It will only advance the minutes at
a grotestquely slow rate. I think it needs about five minutes to advance by
12 hours. Life is simply too short to bother.

If you are still convinced you want independent control, consider other
manufacturers too. I quite like the Horstman stuff, for example.

P.S. the link you gave had prices on the high side. Unless you get some sort
of discount, try (amongst many others) www.discountedheating.co.uk.

Christian.