
On both occasions when I took bitches abroad, I had to book the flight on the day she came in season.
So I aimed at day 12 (usually had bitches mated days 14 - 18) and a return after the season was likely to have finished and stayed for a week with one, and after having one very late bitch (mated days 18 - 22) most recently went for 10 days last time.
I am mating my maiden bitch in Scotland in the coming months and will go up on day 13 and return a week or so later, but only have to book train.