It varied a lot.
The first time, it took an hour or so. My co-founder and I were both working at a struggling company. It wasn’t hard to convince her. The idea to start the company may have been mine, but the technology we started it around was hers, and neither of us had long-term guaranteed jobs. Neither of us had even started a company together, but we went off, talked to all the customers, did 2 months of research, and said, Let’s Go!
The second time, the shoe was on the other foot. It took 6 months to convince me. I’d already sold one start-up and didn’t think I would want to do it again. Startups are just so hard. My co-founder had to nudge me for 6 months, on a variety of ideas, until I was ready to go again. I needed to learn if I was ready for that crazy experience again.
Maybe there are no hard-and-fast rules here.