I actually just went to a funeral
of a guy who did that a few months ago (xanax
and methadone). In fact, in just the last 2 - 3 years in my area I have personaly known 3 people who have died from that, but there have been many many more.
I am not sure how long darvocet stays active, but methadone is a LONG acting medicine and it may not matter if you take the doses 12 or even 24 hours apart. Stay safe!