There are YouTubes about using Windows Task Scheduler to start OBS at the desired time, and adding some command-line flags to have it start streaming and recording immediately with whatever it comes up with. That works without installing anything, but the Advanced Scene Switcher plugin makes it a whole lot more maintainable!
This plugin will allow you to automate various tasks using "Macros". Macros consist of a list of conditions under which a list of actions will be performed. Examples and guides can be found in the wiki. Feel free to contribute! If you run...
obsproject.com
And that only scratches the surface of what Adv. SS can do! One of my rigs has enough macros to automate different things, that I need a separate poster to keep track of them all.
The idea here is to already have OBS running - not doing anything, just sitting there - and when the time comes, it "just happens". Any method to start OBS ahead of time is fine, automatic or manual.