Fleets won't be coming to those who have not received it yet anytime soon as Twitter is slowing down its rollout to the general public in order to fix some performance and stability problems.
Twitter fleets RSS
Twitter announced that its ephemeral content sharing feature, Fleets, is rolling out to all iOS and Android users. With Fleets, users can share tweets, photos, and videos that expire in 24 hours.
Twitter starts testing ephemeral content in Brazil from today. Just like Facebook and Instagram Stories, "Fleets" will disappear after 24 hours of posting, though you can't retweet or like them.