Moving on to watering 200-300ml every 2-3 days until the presoaked 1.5L deep in the soil are consumed, the seedling occupies the big pot and I can water the whole plant normally.
Update:
I realized I got fungus gnats, probably since transplanting to the 10L pots. I added yellow sticky traps to catch the mature gnats and beneficial nematodes to take care of the larvae. With that I'm also switching to watering 500ml every ~3 days.