Well, you can't specify IFTTT routines in Stringify, I think.
You tell it to call IFTTT and IFTTT decides what gets run based on which flow calls it. IIRC.
So, I just made a flow called "Testing 123." Green button -> IFTTT -> 10 second timer -> IFTTT. I do not specify in the flow what IFTTT does.
I move over into IFTTT, I make an app and use Stringify as the "this" I pick the first "Testing 123" from the dropdown. And for the "that" I tell it to turn on a light.
See how there's two Testings 123s to choose from?
Then I make another app in IFTTT, for the "this" I pick the SECOND "Testing 123" from the dropdown. And for the the "that" I tell it to turn the light off again.
I press the green button in stringify, my light turns on, 10 seconds go by, and then it turns off.