I misunderstood what you meant by sleep timer-- I though you wanted a remote which itself has a timer.  To add to mdavej's comment, if you do learn the FFWD and REW functions, the IR command will be sent on button release, so it won't persist for very long.  If you want to have these signals continue while you speed through material, hold the button and the IR signal will start after about 2 seconds.

It is fine to learn the additional commands, and it is also possible to program in signals even if you don't have the OEM remote or want to access a function not included on the OEM remote