From my somewhat limited experience i'd say it can be setup, but reliability will be an issue. The communication between Wemo, IFTTT and Stringify might take several minutes... I think the warning given is up to an hour.
If you still want to try then:
Set Stringify flow with IFTTT as a WHEN and then create and function parameter 'tvstate' to 'Standby'. Give it a sensible name e.g. setTvStateStandby. Then in IFTTT create applet with Wemo switch, standby action and THEN Stringify and pick the Stringify flow you'd created.
Then create a duplicate flow with a the name setTvStateON in Stringify but set the function parameter 'tvstate' to "ON" or whatever else. In IFTTT use the trigger "Switched on" to trigger the Stringify flow.
Thirdly create create a Flow that uses Function variable, Timer, Text Function and IFTTT. You'll have to do WHEN a variable changes > THEN timer, 30s (or a bit longer to improve reliability) > THEN again function variable 'Get the value of variable' > THEN Text Function, 'Continue the Flow if text equals "Standby" > THEN add IFTTT. In IFTTT create an applet with Stringify as IF, choosing the name of this last flow, we've created and THEN action Wemo insight switch Turn Off.
Then cross your fingers.
Let us know if it works.