Giveaways threads typically appear within 24 hours (or much less) if they abide by the rules of that forum.
We'll sometimes try to contact folks to let them know if/why a thread wasn't approved, but due to how busy the site is, we don't often have the time to devote to it, so we generally rely on the rules posted in the forum to do the 'splaining for us even though we realize that can be a little confusing!
I checked your posting history, and you don't have a thread active or in the approval queue, so the thread you submitted wasn't approved.
I'm happy to explain the details of why if you contact me privately to discuss your specific thread, but in general:
Horses/ponies being offered for temporary or permanent rehoming must be free, unless the animal has an adoption fee through a 501c3 charity. In the case of a free lease, you can ask that the horse's expenses are taken over.
We only allow very limited horse wanted requests. Requests are limited to trail riding, companion, "husband"-type, or very beginner mounts. If you're looking for a horse to show, jump more than a crossrail, a "prospect," a schoolmaster, etc., the thread won't be approved.