Why do you want to put a Tivo in standby mode? Unless it interferes with your other devices I wouldn't worry about it. Mine stay on 24x7.

If you need to do it so you can use the TV tuner then setup the Tivo on/off config to put it in and out of standby mode. Then create a watch TV activity that doesn't include the Tivo (only the TV) and tell it you use the TV for changing channels. Then when you're watching Tivo and select Watch TV it will put the tivo in standby mode (turning it "off") and setting the channel buttons to the TV. When you go back to Watch Tivo it will take it out of standby mode (turning it "on") and the channel buttons will be reset o the Tivo.