The broadcast time for Doctor Who has chopped and changed considerably in recent years. Last year saw a much later average start time, which fans wrongly assumed meant that the series would be less suitable for younger children. The expectation this year is that the show will air a little closer to Saturday teatime, with BBC executives admitting that the move to a later time was a mistake. It's something of a myth that in the good old days weekend television schedules were more consistent. Sporting events regularly affect timings and broadcasters have always sought to get one over on the competition through clever scheduling. So if I was you I'd set the digital recorder to series link. Chances are the start times will continue to fluctuate from week to week.