Today, Epic announced the LTM Creator Contest, the winner of which will have their creation (made completely in Creative) featured as an actual Limited Time Mode. To be eligible players will need to create either an Island or a Block using the guidelines provided here.
Once their creation is complete, players will then need to submit them via the Fortnite Creative Content Submission form. Be sure to read over both things carefully to make sure you meet all the requirements.
Submissions will be accepted until April 8. So, if you want to see your creation featured, be sure to mark the date on the calendar.