Hello again :-)
The preparation is established with the coach, a year before the competition. We prepare a program to prepare the horse. You need a program before and after the selection. For me, it was a little bit different between the two Olympics, for the first one, my horse was 13 years old, a normal age, for the second one in Sydney, he was 17 years old. It changed a lot of things for the preparation, we didn't want to tire him before the Olympics.
The two countries in which I participated to the Olympics were far away, with 15 days of quarantine. We had to go there 1 month before the Olympics, so it doesn't require the same preparation as a show in a nearest country.
My horse needed to compete every 3 weeks to stay good, and we had to have 5-6 weeks without any shows before the Olympics. He wasn't as good during trainings as during shows, so we couldn't train so much.