Well this depends on where you live. For most people, its right about End/Mid of May to June 1st. You want to tranplant after the "last frost".
is there a way to judge by how many weeks or by how the plant looks when it would be able to go outside?
The sooner it goes outdoors, the bigger it'll get A plant does not need to be a certain age to go outdoors. Infact, the younger it is, the better.
thanks for the help, should i just stick them in the ground, or would it be better to put them in a big pot for now outside? (i have them in the party cups at the moment)
There are several ways you can do it. The most common is to big a big hole and fill it with good dirt. Or you could get 5 gallon buckets, fill them with dirt and than burry them in the ground. Having the 5 gallon buckets above the ground is very noticeable and could draw attention. It also protects the roots from the heat of the sun.