To hold your horses means to be patient. It refers to the situation where one has to hold the reins of the horse when one gets off, otherwise it could stray away; or holding the horse steady when it gets startled by a sudden noise.
1. The ISC members were constantly posting Forum messages asking for quick review of their posts so the Webmasters requested them to hold their horses.
2. The boss pointed out to Mr. Saxena that he had always told him not to rush into doing things and to hold his horses before starting any project.
3. The teacher told her students to hold their horses and not hurry out of the classroom as she wanted to give them instructions for the exams.