Something of concern: the engine may stall, and if there isn't enough charge in the battery to re-start the engine, you could be screwed in the middle of the traffic.
I'd say some period of idling would be good. Not necessarily 45 minutes, but let it idle at least 15 minutes. By 15 minutes, even if idling (so charging rate is lower), there should be enough charge to start a warm engine and the engine should be warm enough to be easily restartable.
This is especially important if the car is a manual transmission car and you either have a history of stalling engines when accelerating from a stoplight, or if you for some reason are unfamiliar with the clutch feel of the car (for example due to it being a very recent purchase).
Of course you may avoid this problem by giving excessive gas before operating the clutch. It'll burn some clutch, but quite well avoids the possibility of stalling the engine.