It sounds like Mason was actively working on The Point/Groupon for those two years, not just passively thinking about it. He quit his day job in 2006, he was enrolled as a student during the time period, he launched The Point about a year afterwards, he was in full contact with Lefkofsky during the time, and he launched Groupon a little less than a year after the decision to refocus The Point on something that could actually make money.

That's very different from dreaming up an idea and then forgetting about it for 30 years while you work on your day job.

That's the sort of iteration that basically every business needs to go through, though. The great-grandparent post points out Groupon as an example of a business that succeeded in much less than 2-3 years because it started with a business model, and I pointed out that Groupon neither had a business model when it started nor took only six months. This whole subthread started with a question about whether 6 months is adequate for someone just now quitting their day job - it's most likely that someone in that situation is at that "I'm thinking of a web platform for collective action" stage, not at the "I have a web platform for collective buying" stage.