Adding Product To Your Startup Team
There are a variety of reasons this should come to an end....
Some people say you should wait until you reach Product-Market Fit.
If you get immediate traction from your MVP, maybe that will work.
But if you need serious Customer Discovery, a co-founder probably won't have the time/focus to do that, and is probably a little over-committed to the initial vision/plan.
Likewise, this is not the time to hire a "junior" (3-5yrs experience) Product Manager: such a person hasn't seen a broad enough variety of challenges to have the "product taste" necessary to find the path to success.
What should that Product person do when they arrive? Product Management from MVP to Product-Market Fit