"The Counter-Clock Incident", from the second and last season of TAS, was the last episode of the Animated series. Therefore it could be assumed that it is near the end of Kirk's 5-year-misson in the year 2268.

In "The Counter-Clock Incident" Commodore April was a retiring Ambassador aged seventy-five. Therefore he was born some time (2268 - 75=) between 2191 and 2195.

"Twenty years before" (something between 17 and 23 years before) the episode, Starfleet officer Robert April is promoted to Commodore and becomes a Federation ambassador-at-large. That must be some time (2268 - 17/23=) between 2244 and 2251.

He was the first captain of the Enterprise and his wife Sarah April was the Enterprise's first ship's doctor.

And 2252 Pike as the Captain of the Enterprise is contacted by the Talosians.

• April is promoted to the rank of Commodore and in the same year or later the command of the Enterprise changed to Pike.

We already know, that Pike was contacte by the Talosians 2252 and that Captain Pike is promoted to Commodore in 2263 or 2264. There are at least 11 or 12 years carrier as Captain in Starfleet! Therefor we have to think about two 5-years-mission, because three would be to much.

Therefore we can make some speculations:

• Kirk's mission starts 2264.
• Before that there was a major refit at first under the command of Captain Pike; later on under Captain Kirk.
• Pike's second mission could have started 2257 and ended 2262.
• Pike's first mission could have started 2251 and ended 2256.
• April's mission seemed to end 2250. In that year he was promoted to Commodore.
• April's mission would have started 2245.