I'd say it's a given that unless otherwise indicated within the show, an episode should be current with the date on which it was first broadcast. It doesn't have to be that exact same day, but preferably within the span of that month.
Typical exception would be the 'Law & Order' franchise which time-stamps just about every scene. Or Christmas themed episodes of shows which usually air several weeks in advance.
But one thing that should be considered law when it comes to Toobworld's inner timeline - episodes should follow each other in a linear fashion. That is, last week's episode of 'Crumbs' should be followed by tonight's episode in the timeline. Tonight's episode shouldn't precede last week's, unless it was specified to be a flashback.
But there have been two instances in the last few weeks in which such a circumstance happened.
With one, it happened in connection to a new, (hopefully) continuing series of TV movies. Last year, "Stone Cold" was broadcast, an adaptation of the fourth book in Robert Parker's series about Jesse Stone, the sheriff of Paradise, Massachusetts.
Just two weeks ago, a second movie was aired, "Night Passage". But in this one, Stone moved to Paradise to take up the job as sheriff. (Police chief? Not sure.)
The other example came from a new ABC series which I'm enjoying very much - 'InJustice'. With the first episode, Kyle MacLachlan's character of David Swain was firmly established as being in charge at the National Justice Project. But in the second episode, he was just showing up with the intent of running the organization.
The backstage splainin for this is easy. The network decided to open strong with a more powerful episode to hook the audience, and then burn off the pilot during the second week before too many cases were under Swain's belt.
I don't have the stats to back this up, but I think such a situation has happened before in which the pilot episode isn't aired until later in the first season.
But how to jibe such an occurrence with Toobworld's inner reality? If I remember correctly, there never was any indication that 'InJustice' was dealing with a flashback.
So here goes - "Night Passage" and the pilot episode of 'InJustice' happened at the same time, during a point in Toobworld's history in which there was some kind of massive temporal "burp". It happened for all of the other shows on the air as well, but just by sheer luck, none of them had episodes which were occurring at the exact same point in Time as those two examples.
And who was to blame? More than likely The Doctor, causing some kind of rift as he and Rose returned from the alternate dimension in which Harriet Jones is the Prime Minister of England. (As seen in 'The Christmas Invasion' - there's nothing to say they left the scene of the Sycorax invasion straightaway. They probably stayed around a bit to celebrate the holiday with Rose's Mom and Mickey.)
That's my story and I'm sticking to it. Um... unless you can think of something better.....?