In order for a webthing to also control other things, you’d need
to interact with the gateway’s REST API, which is definitely
possible.
You could also use rules (and perhaps the pulse adapter to allow
for your delay), if your webthing exposed a propert, which when
triggered sent the serial commands to the receiver.
It really depends on how transparent you want things to be.
You can do some rather interesting things by creating webthings. See http://www.twobraids. om/ for some
interesting examples that can be done with some more interesting
custom web things.
A webthing can create arbitrary events. For example, push
buttons might create a “pressed” event. The event by itself doesn’t
do anything, but you can create a rule which uses the event as a
trigger to perform some other action.