It's definitely odd for this kind of news to be announced so early, but director Michael Bay has revealed that Transformers 4 will have a runtime of 2 hours and 7 minutes, which is a little less than the previous movies but not by a whole lot (Dark of the Moon was 2 hours and 35 minutes). Even though Bay was very specific with the runtime, it is subject to alter slightly since filming hasn't even started yet. On that note, after discussing the runtime, Bay gave an actual time when filming will begin: 5 weeks. The first location will be Hong Kong, followed by other places in China, Detroit, and Chicago. Expect other locations mixed in there as well. Below is the translation from a French article which can be seen by clicking the above link.
"Two hours 7 minutes, which I think is a good formula, which gives enough
room to maneuver."
Shooting begins in five weeks in Hong Kong and
will continue to other places in China, Detroit and Chicago.