Add this Lua code to the scene:
local DEVICE = 21
local SECONDS = 1
function turnOffDevice()
luup.call_action ("urn:upnp-org:serviceId:SwitchPower1", "SetTarget", {newTargetValue = "0"}, DEVICE)
end
luup.call_action ("urn:upnp-org:serviceId:SwitchPower1", "SetTarget", {newTargetValue = "1"}, DEVICE)
luup.call_delay ("turnOffDevice", SECONDS, "")
This turns on your DEVICE and after SECONDS seconds turns it off.