UKC

Can't find anything online. There seems to be hundreds of power sockets around that I could control via Alexa, Siri and and all these other smart devices via wifi, which I don't want. 

What I do want is to have an app on my laptop that will switch said sockets on and off on a schedule via the home wifi.

Am I looking in the wrong place or has nobody thought of it yet?

Tasmota

You need to change firmware in the smart socket, see tasmota.

Mihome / energenie

although it is the homegateway that does the switching on a schedule, rather than the software running on a laptop

they do provide a good api if you want to write your own app

Laptops aren't powered on 24/7, cloud services are.   If the laptop isn't switched on itself control software running on the laptop isn't much use for turning on other things.

The laptop I have in mind is already on 24/7.

Sonoff S20 with Tasmota is the one I see most so I got an S20 but haven't got round to reflashing.

On a popular auction site you can get S20 and S20 flashed with Tasmota.

https://github.com/arendst/Sonoff-Tasmota/wiki/Commands#timers

You can set on/off timers in the plug itself so the laptop does not need remain switched on. 

Raspberry Pi for a 24/7 non-cloud interface if you want access away from home.

I use "smartlife" app via android. does everything you want, without needing alexa or any other voice assistant (although they are compatible)

I'd be surprised if there wasn't a windows app for it. even if there isn't you can set-up timers etc and/or manual override from your phone

You need cloud computing man. 

This looks interesting. Do you know if I have to register and control things online, or can all the scheduling be done 'in-house'?

Mihome looks like IFTTT which is register & use cloud service, not "in-house".

Getting an open API like you want is annoyingly difficult.

What make are the sockets? They usually all come with some sort of app to control them.

I don't have any sockets yet, I am looking for some to buy which will have a Windows programme to control them.

Not sure if you have an android phone or not, but if you do, the programmes for controls lives in the socket, it doesn't need to be connected to a control device e.g. a computer  or phone to enable it to work, only to set it up.

If you want to switch it on and off manually then it needs a connection to your wireless network and some device.

One of mine controls a light which is switched on and off 30 minutes before and after sunset and sunrise, it adjusts this with the lengthening days because you can give it  a longitude and latitude value.

The only time I've connected to it since setting it up is to override it, and that's because I was too lazy to walk the 2m and press a button on it.

Finally got round to flashing Tasmota onto Sonoff S20. 

Tasmota comes with a basic web interface for setting timers in the plug.

The timers then run independently with no input from your local laptop and no reliance on a cloud service.

Tasmota has MQTT but I just used http interface. 

 PS take care with UK version of the firmware, that's Ukrainian. I should what UK means by now!