Some time back when I was new here, my posts got 'reviewed & approved' by moderators before they would appear on the forum... sometimes took a day or more.
Posts from new users containing links or photos are sent to a moderating queue. It’s an anti-spam and anti-abuse measure and has been in place for many years. Most of you never noticed.
So, the answer to the question is “as long as it takes for one of the moderators to see it in the queue and get to it”.