When is a business cofounder needed

I am technical founder right now of my own software startup.

Right now, I'm developing the software and am seeking a business cofounder.

I lack domain expertise in the various parts of the business side of a startup.

I am willing to learn it, but I cannot do everything (as I've recently had to learn myself).

I am talking to one particular business cofounder (business/marketing end), but he basically doesn't want to join yet because there is no product yet (I'm pounding my fingers working on it). Is this guy likely not the right business cofounder for my startup?

Ideally - while I'm busting my butt to develop, he could be busting his butt to realize our first clients, including beta testers, proper marketing/sales etc. There is no question the product in MVP form will be ready by May/June of this year.

Is this a realistic view of a business cofounder at this stage (pre-product) or is he right in not joining until a product is developed that he can sell?

Not wanting to join before the product is completed is bit of a red flag.

If you read all the lean startup approaches, customer development is needed to better shape what the MVP would be - as well as the price one would pay. This video quickly describes the pros behind customer development. Identifying problems worth solving and creating a working business model are as important (dare I say more important) than what you're coding.

And yes, it's a lot of work as well. But customer and product development efforts feed each other. The straight line approach (code / finish / QA / market / sell) sounds like what the other "founder" is following - which I will leave to you to determine whether that is the approach you wish to pursue. If you like the customer development approach, books like running lean, startup owners manual and the lean startup should give you some ideas.