If you press the Power button while the Toppy is recording it will give you a "Power Off" prompt asking you to confirm this choice. If you select "Yes" then it will stop all current recordings and go into standby. If you select "No" (or press Exit) then it will cancel the power off and remain on. But there is a third option: leave the prompt alone. If you do this it will automatically go into standby once all recordings have completed.
Another option is to use the Sleep Timer to do a timed shutdown. Ordinarily the Toppy will power off once the set time has elapsed, but if there are recordings in progress it will wait for them to complete first.