In all the juridictions I have worked in, the code I ship during my work hours is owned by my employer, not me. I simply just can't decide on my own to contribute during my work hours. I need a formal agreement to work on open source code, and every single time I asked for it it took so much time (months) to run through legal department that I simply gave up or another contributor had shipped a PR in the meantime so I just gave up asking.
This point is obvious to devs with more experience but has been a real problem with some junior devs at some of my companies: They see something cool the company is doing in an internal project and think it would make a great contribution to some open source project, without thinking about the problems with using their knowledge of closed-source code to submit substantially similar code (or in some cases, copy and pasting) to an open source project.
Most employers that are not IT focused wont even understand what open source is or how it works. So I guess it's hopeless for many to get permission.
The linked site should probably focus on explaining benefits of open source and advocate legal guidelines for _employers_ primarily.
Same in most countries I worked in. Generally it's not just the business hours, but also any kind of device used. If code got edited at one point on a company laptop, or during office hours, then it's the company's.
Most intellectual jobs in quant finance will also routinely enforce an intellectual property clause in their work contract, which extends appropriation to anything resulting from the knowledge you acquired at the company. Not sure if that is enforceable in practice, but it's always there.
This AFAICT, isn't the case where I live, I usually have to sign something actively giving the the employer ownership (And usually it's scoped to the project), but I'm not sure if this is a formality
That would definitevely count as company time and company device usage.
*: for common values of ownership in german copyright law
That would be relevant, for example, when the company goes defunct, and no one else holds any usage rights for the work. Then you'd regain those usage rights.
That of course is iffy to make use of because you'd need to be sure that you are considered the exclusive author, and that no one else acquired these exclusive usage rights.