Those aren't 15,000 seater permanent sustainable-wood-framed structures, like the York proposal (if I recall correctly). One was already a permanent stadium that got expanded, and one is a temporary popup that is on a trial basis and I think has to get partially torn down every winter? Very different situations.
5+ years seems about right to me as well. At least a few to get going, make sure it's somewhat sustainable, and market research. And then a couple for land acquisition, design and construction.
(Some design could happen now but it will be constantly changing based on the gathered info and feedback)
Edit: I also seem to remember them being pretty clear that building a stadium was few years away, from the very start