Go into your compose tweet screen
Once you have typed in the tweet you wish to post later, please hit your menu option on your device and select "Post Later"
Once you have selected "Post Later" you will then be presented with a date/time option. Please feel free to select the date/time you wish to post the tweet and click ok.
If you need to remove a scheduled tweet, click on the scheduled tweets icon in your compose tweet screen and click on the (x) to void the scheduled tweet.