I prefer joining startups later after a year or two, or if it’s not bootstrapped, after the second or third round fundings. Here are some reasons why.
After a while, time will tell whether it’s a product market fit. This saves the designer some time and let him really focus on products that’s really useful for its customers.
Processes are in place. Human resources, finance and product teams are in place and have a working process. This proves the commitment of the founders that they’re really learning about management and are keen in establishing a good foundation for the team.
Money matters. It will prove whether the founders are either sloppy or wise with money. Do they have a vision of where the money should go? Look at the composition of the team and company assets. If they are bootstrapping, do they already have revenue coming in?
Culture fit. It shows how the company commits to building a positive and productive culture.
Solving a bigger (and more focused) challenge. By the time it’s baked half-way through, you will know what problem lies product-wise and what should be done about it. It makes your case stronger when you present a solution, because the “user acceptance test” has been done.
Team is built. By a year or two, the team will be more “stable” than it is in the beginning. It probably already has a CTO or technology lead, some senior or junior developers, some designers, and some other sales or marketing. This makes it easier to execute stuff. If the team is not built, don’t bother joining.
In general, by joining later in the stages, I will know whether the startup is for long-term or otherwise, be it people-wise or product-wise.
If I want to jump in early in the establishing stage, I’d rather be a co-founding member or when I know the founders personally.