@Timo
Regarding Space Seed's placement, I'm utilizing the Memory Alpha date of 2267 for it.
It's generally presumed each season equals a year of the 5 year voyage. Season 1 lasts from 2266-2267 (though The Cage is set in 2254 and Where No Man Has Gone Before in 2265), Season 2 is 2267-2268, and Season 3 is 2268-2269. If you view TAS as canon, that has Season 1 in 2269 and Season 2 in 2270 (again per Memory Alpha).
The thing is, the Stardate system utilized in TOS and TAS was ambiguous to the point of not even being applicable, so can't be taken as law. If you were to organize TOS and TAS by Stardate The Magic of Megas-Tu would occur even before The Cage, which makes no sense as Pike is commanding in The Cage, and Kirk is commanding in Magic of Megas-Tu, and we know Kirk came after Pike. Granted you could ignore TAS completely but even then, the Stardate system is full of holes in TOS era. This does a good job of listing the Stardates and illustrating how random they were in TOS era:
http://www.johnstonsarchive.net/startrek/st-episodes-1.html
We have Stardates ranging from 1300-5900 during TOS (a period of 3 years), then jumping to 7412 for TMP, and 8100-8400 for II-V...
But, if only 2 and a half years pass for a jump from 5900-7400 (between end of TOS Season 3 and TMP--a period of 2 and a half years equating to about 1500 Stardate difference), then 7400-8100 (between TMP and STII) something doesn't add up (a period of 13-14 years with only 700 Stardate difference).
The point is, Roddenberry and TOS/TAS writers left Stardates intentionally ambiguous. They were never really meant to reflect a chronological order, and were apparently largely chosen at random. It wasn't until TNG era where they normalized the approach.
As for Enterprise-A, it's clear in the film that they return from the past with the humpback whales, face trial, are exonerated and assigned to the new ship. There doesn't seem to be any viable placement to insert a year or more time. Presumably the construction of that Constitution class ship was already well underway before the first Enterprise's destruction and it was simply renamed Enterprise-A to replace the lost original. Maybe I'm wrong but I just watched the film yesterday and the trial leads directly into them being assigned the new ship and going up to see it and take it out of spacedock for a test run.
Regarding Space Seed's placement, I'm utilizing the Memory Alpha date of 2267 for it.
It's generally presumed each season equals a year of the 5 year voyage. Season 1 lasts from 2266-2267 (though The Cage is set in 2254 and Where No Man Has Gone Before in 2265), Season 2 is 2267-2268, and Season 3 is 2268-2269. If you view TAS as canon, that has Season 1 in 2269 and Season 2 in 2270 (again per Memory Alpha).
The thing is, the Stardate system utilized in TOS and TAS was ambiguous to the point of not even being applicable, so can't be taken as law. If you were to organize TOS and TAS by Stardate The Magic of Megas-Tu would occur even before The Cage, which makes no sense as Pike is commanding in The Cage, and Kirk is commanding in Magic of Megas-Tu, and we know Kirk came after Pike. Granted you could ignore TAS completely but even then, the Stardate system is full of holes in TOS era. This does a good job of listing the Stardates and illustrating how random they were in TOS era:
http://www.johnstonsarchive.net/startrek/st-episodes-1.html
We have Stardates ranging from 1300-5900 during TOS (a period of 3 years), then jumping to 7412 for TMP, and 8100-8400 for II-V...
But, if only 2 and a half years pass for a jump from 5900-7400 (between end of TOS Season 3 and TMP--a period of 2 and a half years equating to about 1500 Stardate difference), then 7400-8100 (between TMP and STII) something doesn't add up (a period of 13-14 years with only 700 Stardate difference).
The point is, Roddenberry and TOS/TAS writers left Stardates intentionally ambiguous. They were never really meant to reflect a chronological order, and were apparently largely chosen at random. It wasn't until TNG era where they normalized the approach.
As for Enterprise-A, it's clear in the film that they return from the past with the humpback whales, face trial, are exonerated and assigned to the new ship. There doesn't seem to be any viable placement to insert a year or more time. Presumably the construction of that Constitution class ship was already well underway before the first Enterprise's destruction and it was simply renamed Enterprise-A to replace the lost original. Maybe I'm wrong but I just watched the film yesterday and the trial leads directly into them being assigned the new ship and going up to see it and take it out of spacedock for a test run.