You have to put the video on "private" first and then "schedule" option will appear 
-
-
-
Thank u Rey, it worked


End of conversation
New conversation -
-
-
We'd like to look into it. Could you try uninstalling the app, restarting your device and reinstalling it? Let us know if that makes any difference.
Thanks. Twitter will use this to make your timeline better. UndoUndo
-
Loading seems to be taking a while.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.