When is the right time to incorporate your startup?

I am aware of https://news.ycombinator.com/item?id=16093966

But I couldn't find any guidance for my case, which I think is actually not that uncommon:

I'm your typical Silicon Valley tech founder and I've spent some time building a prototype and designing a system/service. This prototype is enabling me to get potential partners interested, and I could certainly use their help to turn it into a product.

I'm trying to find ways to compensate them for their help, but without cash (for obvious "no cash" reasons). If I had a C Corp today, I'd probably be able to structure a contractor agreement that compensates them with equity, but without a C corp, I'm not sure what to do.

Ideally, I'd like to set up some kind of agreement that says, in layman terms: "You work on this project on a X hours a week basis, and in return, when we incorporate, your share allocation will be Y%".

If I incorporate now, it'll cost me a couple thousand dollars (even through the Stripe Atlas route) and some headaches that I'd like to not deal with until "the right time", so I can focus on building the product, while minimizing losses (time & money) if the project hits a dead end before launch.