Originally Posted by Sceptilianus:
“Between a 6PM timeslot and a non-existent marketing campaign - it looks like the BBC's plan for doctor who to get a sub-5million overnight rating is going well.”
The trailers (as has been widely discussed in the DW thread as I am sure you know, having taken part

) generally start two weeks before transmission, with teasers (which have aired) between three and four weeks before transmission. Granted some series trailers have started a bit earlier than that, whilst others have been within two weeks of the broadcast.
The first proper trailer airs tonight on BBC one
As for the time, all DW fans know full well that it should be kept to a standard 7pm or thereabout slot, but that it will be moved about each week (sadly). But that it also has massive timeshifts which generally make up for any losses in overnights (which are far less important to the B BC than they once were, now that timeshifting & iPlayer have evolved).