Not sure if will give you tight enough control but I have been using the Power Allowance feature to turn off an outlet after a set period of time - set in minutes. One app turns on an outlet that controls a space heater if my garage is too cold, and the power allowance turns it off after 45 minutes.
Dave
Unfortunately I don’t think the native ‘power allowance’ app will not let you input less than a minute.
Rob is wanting 20-30 seconds
Btw… I have an app for your garage heater too 
(Assuming you have some kind of temperature sensor in there)
I know this is already answered using a software solution but for a hardware solution you can use a “one shot” relay. In essence when it gets triggered it will trigger its own output for xx seconds then turn it off even if power is still being applied. Then when power is turned off it resets so it can do it again. The other hardware solution would be using Konnected or ST_Anything since they both support a momentary output with selectable time.
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Rob
I have updated the files on GitHub as promised (not promising that it will work on Android though!)
There is one thing to confirm…
When you click on the Github Link for the file
you MUST click on ‘RAW’ before you copy the code.
This will open in a full page browser. - CTRL + A to select all then CTRL + C to copy.
This can then be pasted into the IDE (the same as last time)
Hopefully this should work OK now…
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I just completed a similar project using an Inovelli dual outlet module. However, I opened and modified it such that I can now control 2 garage doors and get power through on the outlets (they are not controlled any more).
Then I created 2 Simulated Momentary Tile for ST control and a Webcore piston to make it work.
It also works on Presence.
yup, works perfectly now Andy, thank you very very much for your quick solution to my little project. You are awesome!
Rob
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This is an awesome community…its greatest strength is not the HW, SW, FW, etc., it’s the helpful people here like you, Andy.
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Link to the relay you are using?
You are welcome Rob.
Glad we finally got it to work for you…
What you want now is for it to open when you get home and close when you leave 
lol, maybe so. But I’ve been fooling around getting my Vivint panel connected to ST. I’ve got it linked through Google Assistant, so I can voice command the door to open ! and arming / unlocking through GA now.
Just have to fiddle with getting a Arming Away action on my ST
Thank you for your kind comments Dana
I was helped a lot when I first got my hub so it only seems right to give back if I can
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Rob are you using SHM or do you just set normal ‘modes’?
sorry Andy, I’m not sure exactly what it is your asking (still new to all of this terminology and technology).
Are you asking if I’ve got the Vivint panel to appear on my Smart Home Monitor panel?
If so, then no. I;m just able to control some of it through Google Assistant
I echo Dana’s comments Andy.
I see that this community actively supports everyone with very helpful and knowledgeable replies from experts like you .
Beginners like myself greatly appreciate your help and your patience.
Ah!
I just googled the panel… now I understand why you were talking about ‘arming away’ I thought you were talking about smartthings SHM (Smart Home Monitor) which also has an armed/away mode.
Just ignore me… I’ll go away now 
Rob to be honest, in the big picture, I’m a real beginner too (but I can do the simple stuff)
I’ve had my hub for around a year and have picked up a bit of coding along the way, but im not anywhere in the league of some of the guys here… still learning though.
I decided at the beginning that I wasn’t going to use core or webcore but try and learn the code as a bit of a hobby.
Well I’ve pretty much got my system running how I want it so not much to do now
(even my very tolerant wife is reasonably happy) 
well that’s something to look forward to for my journey. If I can make it easy and painless for my wife to use it, then I’ll consider it whatever the final product to be as a success too !
As for the programming side, I tip my hat to you and anyone else that learned how to put it together and make it run. After you signed off last night, I looked into the tutorial on ST page going through Groovy. And I’ve gotta be honest with you, I made a couple of attempts at understanding and learning some type of coding and it has never clicked with me, maybe I’m never going to get it to click in my head, so its great that you have made that connection and get it.
Maybe I’ll just have to get you to make all of my apps in the future ! LOL 
Rob,
probably the 1st real thing to get her on my side was the house announcing:
“I thought you might like to know,that the washing machine has finished its cycle”
When she heard this for the 1st time the look on her face was priceless (she did roll her eyes afterwards though)
I’m lucky that we have both been in IT for more than 20 years and she is almost as much a gadget freak as I am.
BTW (any folks reading this)
Please don’t think I’m being sexist regarding the washing (laundry) As I work from home most of the time I do it!
As for making your future apps… I’ve probably already got them somewhere 
Having seen some of @Danabw posts in the forum (I note she is also very helpful) I believe she uses webcore for most of her automations and announcements.
I’m sure Dana would be able to give her thoughts on using this instead of coding smartapps
OMG, I need that washing machine app !! lol, I’m sure my wife would roll her eyes too
Thanks! I’ll check it out.