While a decade passed between the last episode's filming and the release of TMP, "in-universe", the elapsed time was between 2.5 and 4.5 years from the last episode to TMP. If, as is most commonly done, you take the last episode as at the end of three years into the five year mission, then two more years of that mission elapsed (some of which was in TAS), the ship returned home, refit began and TMP picks up 2.5 years from coming home (so 4.5 years from last episode of TOS). Some people view TOS/TMP as the complete 5 year mission (just not all shown on screen), so then TMP is 2.5 years from TAS. Others view TOS episodes as the complete 5 year mission (presented over three years), so TMP is 2.5 years from last episode of TOS. However one chooses to view it, the "in-universe" gap between TOS(TAS or not) and TMP is well under the 10 years in real life. The look of the actors in TMP barely lets this gap skate by, so there was a major time jump between TMP and TWOK, to bring the real life and "in-universe" gaps more into line.