In what order do photos and videos appear on hashtag pages?
At the top of some hashtag pages you may see a section called Top Posts. Top posts appear on trending hashtags to show you some of the popular posts tagged with that hashtag.
In the Most Recent section, photos and videos appear in the order that they were posted.
Keep in mind that if you add a hashtag to a photo after it was posted, the photo will still appear on the hashtag page according to the time it was originally posted, not the time the hashtag was added.