I usually wait a good few days before riding a new horse. I figure with new people, new horses, new surroundings, and the stress of being taken away from everything they're used to is jolting enough for a horse without trying to perform under those conditions as well. I understand that many people who show (I don't) need their horses to be able to adjust to any situation and work so I do think it just depends on what your using the horse for. Even if I were though I figure at a show at least the horse has someone they trust and are familiar with (the rider) rather than having absolutely nothing familiar. I just brought my new mare home last week and the stress of working out a new pecking order/a certain gelding deciding he thinks he's a stallion was enough stress for all of us for the first little while lol. In your case though I would definately have given him about the amount of time that you did, you do want to give him a thorough try out after all.