Hi,
As "Deadwood" is created and shown on HBO in the USA, HBO never force time-constraints onto the show's creators. (unlike the normal US time-constraint, where every show must run to 42 minutes, excluding adverts, so that it can be run in an hour-long slot!) Hence, you will never find any show of theirs (e.g. The Sopranos, Oz, Deadwood, etc) with two episodes running to the same duration. (As an example, some episode of "the Sopranos" have run as short as 55 minutes excluding all ads, and as long as 70 minutes excluding ads!)
Deadwood, like The Sopranos, normally runs to about 65-70 minutes, excluding any ads. However, each episode will vary! Some will be nearer 65 minutes, and some closer to 70. As such, each weeks running time, when shown on Sky 1 or Sky Mix, will also vary. Hence, the allocated time-slot will always be somewhere between 70-80 minutes, including ad breaks.
Your best bet, is to always set your video/DVD/Sky+ recorder to allow a minimum of 80 minutes for each episode of Deadwood, if you want to be 100% certain of catching it in full. If the start time is 10pm, then the show will have ended by 11:20pm. If the start time is 11pm, then the show will conclude by 12:20am. See what I mean?
I hope that helps.
Pooch