When should I transplanted to 3 Gallon pots?

Those look like they are ready to go into 5-7 gallon pots , Remember that transplanting your plants will send them into shock for a few days and some plants all together don't like it at all , The less transplanting the better this way you avoid root damages and unwanted plant stresses. You could even go from a starter plug let it sprout gain a bit of root and put it in a 5 gallon right away this way your roots have room to expand and grow vigorously! -Happy Growing!

Hello ! It's up up to you but for me you can transplant when you see the roots on the bottom of the pot. I hope it will help you 😁✌️