When is the right time to transplant into a bigger...

well basically you want to optimise the root growth rate right? so that's why bigger pots straight away actually hinder the growth rate just a bit : the plant grows and grows outwards instead of making that root zone densely. You're already in 1L pots though, 3 weeks later i do think you're ready to transplant quite soon. The truth is there is no right answer except to say that you should transplant before the plant gets root-bound and shocked . that means you shouldnt really wait longer than 4 weeks, that's one more week, you can transplant now or anytime from now. Manifolding or whatever wont really change that actually. When you do transplant consider using mykos and beneficials to kickstart the rooting process, and always double and triple check your pH , substrate and feeding temperatures because these could shock the plant worse than needed. if you see roots poking out of the bag, then it's time to move the plant. Hope this helps ! 🚀