Personally, I've never given much thought to the passage of time because TMP and TWOK are so fundamentally different from one another. I've often considered TWOK to be the TRUE first Star Trek film because the characters (with the exception of McCoy) felt so off to me and the movie was so cold in its portrayal.
Sometimes however I think it does little service to Trek to seek out one specific or definitive explanation, in this case, because the two films are so different.
Nick Meyer's Trek is so different from Roddenberry's Trek, I don't even try to reconcile them. In Meyer's Trek, Starfleet is virtually all military, and David even refers to them as "the military" without, I think, any facetiousness or exaggeration. Also, I think Kirk's story works better if you disregard his character arc from TMP and consider TWOK Kirk an adaption, a retelling of the TMP arc. In both TMP and TWOK, Kirk has become an admiral but still longs to return to the big chair. For me, TWOK arc works better if Kirk hasn't been in the Captain's chair since TOS. The way the arc was played in TMP, I don't think that Kirk would have given up the command chair.