Second time: 5 months
I am coming up to the end of my personal runway on this current venture but I raised some money from friends and family and I'm able to pay myself a little bit now! Meanwhile I know people who are sitting on 4,5,6 years of runway and are still just talking about doing it. Whatever it is, if it excites you and you can convince others of that, go do it today!
I'd suggest about 6 months of runway to be safe, but we aren't doing this to be safe are we?
I think six months is good because it is enough time to figure out if something isn't going to work while being short enough to not be an insurmountable challenge to save up for. I don't have a family yet so there is bias in that number, I would probably say 12 months if I was helping to support one.
Market validation in 1 month, very strong traction with no marketing. Spent 6 months trying to find investors.
Started borrowing lots of money to keep it afloat. It had good revenue but not a profit (e-commerce profit margins were around 6%). Couldn't get investors despite two accelerators, so we sold off the company after 14 months. But we made a good profit even after paying off debts.
Second time: years(?)
Ended up trying to do too many features. Still "wasn't ready for launch" 9 months in, ended up building features with no market validation. I ended up quitting the company because no progress was being made.
First and second startups were essentially the same, except the second one had a much bigger team, more ambitious.
I'd say keep your runway as short as possible and try to launch something by 3 months.
Although if I were giving advice to someone else doing a startup where it's difficult to get immediate traction (e.g. hard tech, enterprise SaaS, hardware, etc.), I'd remind them of the Jason Lemkin rule that it typically takes 24 months to get anywhere[1].
[1]: https://www.saastr.com/if-youre-going-to-do-a-saas-start-up-...
i am proud of it, but i don't think it is startup, maybe just a side project.
Btw, that was personal runway - i.e. didn't get paid for that period. Rather than raising 12-months of getting paid.