Sleep timer? Is that a Roku TV you're talking about?
Always list the model (to include model number) of the Roku device you're talking about. There are enough differences between certain ones that it could be very helpful when troubleshooting.
DBDukes
http://www.dbdukes.com/
Roku Ultra (4660)
Roku Streambar (9102)
Roku Streaming Stick+ (3810)