Excuse the top posting but this thread has degenerated and I want you to get
this problem fixed. Your trouble is in the central office. I had this happen
on my line but it happened during the day when I was at work. I was on vaction
one week and it happend every day at the same time. Since my dsl never went down
and I know telephony I soon realized that the OE or office equipement that gives
dail tone was going into trouble at certain times every day. You will have to
escalate your problem to a manager and ask them to make a routine maintanence
change of your OE. Say it just like that and they will understand. Tell them
the dialtone goes but the dsl stays. Same cable pair so if it were in the cable
outside of the CO then your dsl would go down or you would get a busy when you
called during no dialtone times.
If you cannot get their attention the you can go to your state's regulator
agency and they can get your diatone fixed.