Noob question about transplanting

I planted my seeds about a week ago in 16 oz red solo cups. When I checked on the plants I noticed one where one single root is coming out the bottom of the cup. I have kept the cup sitting in a little water so the root doesn't dry out. I tried to see if the plant is root bound but I didn't notice and other roots.

I'm thinking about transplanting it into a 1 gal. pot in a mixture of VermiFire soil, Coco, and vermiculite.

My question is: Is it too early to transplant the plant? Should I transplant all 4 today?

2 of the plants have their first leaves and first set of real leaves and the other two only have their first set of leaves.

I look forward to reading your responses.

I'd leave them until a good 6-10" tall.
You'll always get couple feeler roots pop out the bottom but that's not an indicator that she's ready for more soil. Its important to transplant at the right time for best veg growth.

They'll explode into new pots, if transplanted at the right time.

If you transplant too early you could have issues with over watering right out of the gate. When my solos are taking water/nutes every 2 days, they're ready.

Thank you Pdx for the tip. I will just leave them be.

That's some great advice right there,let the rootball basically fill the container before transplanting up,its definitely too early from what you say about the foliage above.Let the plant tell you when its time for a new home.Depending on temperature of course,I normally water every third or fourth day when a plant is settling in.I do this because that's when the soil becomes pretty light not because I have a set regimen.When the plant is needing water every other day because the soil is drying that quickly,thats when I know its time to upsize.I prefer going from my starting container to a 2 gal nursery size container.NSI are such common pots people use a 2 gal nursery NSI 600 size is actually 1.6 gallons.These are the pots I sex the plants in.Let them grow into those pots well and with a good magnifying glass after 3 weeks or so,you should be able to determine preflowers.Then it's either 3 gal or 5 gal from there.I used 3 gal for awhile but after trying 5 gal nursery size I saw the big difference in yield and didn't have to water quite as frequently as in the 3 gal.With NSI pots the 5 gal are the smallest pots that have built in handles too,I just think its a lot better deal to go 5 gallon.Of course the space determines it all really,if you have the space and can flower in 5 gallon NSI 2000's,your yield will be so much better