Huge topic. I could probably write a book about this.
Some of it largely depends on the business "phase". In other words things are different if you are pre-launch with no product vs. post launch with some traction, etc.
One of the biggest problems with non-tech co-founders is when they assign themselves far more value than they should. This typically happens when a non-techie has a tech idea and they seek out a tech co-founder to make it happen. I've had cases where people had an idea, no money, no idea how to raise capital, no marketing skills, no management skills, no business experience and a job they could not quit and yet demanded 50% of the startup. In other words, the "tech" co-founder would have to do it all yet the would be valued equally simply because someone without a clue came up with an idea. Run away from those as fast as you can.
In an ideal universe you can't have a co-founder who has zero tech background. It's going to make things very difficult. This person has to have a reasonable understanding of the domain you are trying to address in order to be able to have sensible discussions and make the right decisions. As a technical co-founder you don't want to spend half your management time educating your partner. The relationship has to be symbiotic, and this requires a high degree of overlap in the skill set.
In my opinion it is a far better idea to find a tech co-founder who has an interest in business rather than a non-tech co-founder who might be challenged in learning what he/she needs to learn to make the business go.
I've had the experience of coding 16 hours a day while my non-tech co-founder pretty much just sat there twiddling his thumbs and surfing the web while the product was being built. Useless. Never do that again.
To some degree business isn't hard to learn. You can certainly devote a fraction of that 25% of time you were going to devote to educating your non-tech partner towards learning about business.
Some of it depends on the nature of your market. Many years ago I decided I had enough. I had to take control beyond tech and run the business. I took a two-pronged approach. First, I bought a pile of business books. I devoted about half an hour each night to reading these books, typically at night in bed. I took business books with me when going camping.
I made sure I was learning about business whenever I needed a break from tech stuff. You know how sometimes you reach a mental block while working on a design? It is often better to take a break and come back to approach it with a fresh mind. I these cases I would grab a business book and go read it at Starbucks. In other words, learning about business never ate into my engineering duties.
For about two years the going joke at home was that I had more business books by my bed than technology books. And it was true.
The other approach I took was to have our reseller network educate me on sales. Rather than have them handle sales calls I'd ask them to let me handle them. I would buy lunch after the customer visits and ask that they critique my approach. The first three months were horrible. I sucked at it. I "sold" like an engineer. Which means I had no clue how to sell anything. It took about six months to make the transition and about a year before I could walk into a presentation, say only what was necessary and close deals. Some of the biggest deals I closed required not much more than showing-up and greeting everyone in the room while gently guiding the customer into selling themselves. Magic.
This approach isn't valid for all markets and situations. And, I'll admit to be biased against having a non-tech co-founder in a startup. I've seen ugly things that can happen when you have such a pairing. I'd rather see a pair of tech founders who are able to transition into hybrid roles.