When to transplant these seedlings

It's been about a week since sprouting and these seedlings are in very small starter pots only a few inches wide about same size as solo cups. When is the best time to transplant them into a bigger intermediary pot? I keep reading conflicting info. Some say transplant when the leaves are wider than the pot, which they already are. I can also see some roots at bottom of pots... Thanks

If you see roots out bottom your are probably good to uppot. That being said doesn’t mean you have to right away.

I'd leave them another week. What are they?