I simply read it a week ago and connected the dots while reading opinions from other people in various place, and it fit, "somewhat". The wikia also have a handy (albeit difficult to read)
timeline which points out where the events of SG0 fits in the general timeline. There is also that
very thorough explanation about the ending and why Operation Arc Light is as important as Operation Skuld.
But as I said, this makes sense in the VN, but the anime is a bit loose, because the world line change occured in the middle of his discussion with Maho there, so as you said, it is a bit difficult to imagine Okarin having enough time to contact Amadeus a second time before being overwritten. In comparison, Okarin got his reading steiner reaction while discussing with Katsumi and Kaede in the VN, so there was way more time for the previous Okarin to apologize to Amaedeus in that context.
The only thing I'm still not sure about is how the USSR world line could end after a month, considering there was obviously not enough time for Startfor or DURPA to have enough information about people with the reading steiner to be aware of a world line change to counter the Russians. This is particularly weird because the Americans needed the cooperation from the Japan government to get Okarin and the other persons with a potential reading steiner like Katsumi. So I have hard time to believe it was them that could fix the world line change caused by the Russians.