SaaS founders, how long do you take to build the first versions of your SaaS?

I’ve been building all my mvps in 2-4 days and if I don’t know what to build it takes a week maximum but most SaaS founders I know(Some with more success than I) take a month and 2 weeks or even more than that. I’ve been following YC advice to build things really fast and launch it, even if it’s a bad product. I was wondering here, am I doing it wrong by creating it really fast like this and launch asap?