To be honest, I don't really think it matters anymore. Whereas the first season (and to an extent the second one) was praised for it's real-time formula, it's pretty much been thrown out the window recently. For example, Jack has been able to travel across the entireity of LA in a car in 20 minutes in Seasons 4 and 5. Whereas there are still fans that are moaning about it, most don't really care anymore (myself included).
It's also apparently going to be set in London, or at least part of it is. Disregarding the real-time formula gives them one advantage, it allows them to travel.
I'm all for it. A movie bridging the gap between seasons 6 and 7 is a great idea, and is a better idea than using a mediocre PS2 game to do the same.