The content you post as a Story on Instagram no longer has to be from the past 24 hours. Instagram has updated that portion of the app to include support for older content. Stories now lets you browse all of your photos and videos, with the option of posting whatever you want.
By default, Instagram adds a sticker with the date the content was captured to your Story. You can resize or remove that sticker if you want to.
We learned of this potential update a couple months ago and now all users have access to it.