how long can i keep clones that have rooted under low light?

i got roots on some clones and wont be ready to veg them until 40 days from now. i was thinking about putting them in styrofoam cups until im ready to veg. how long can i keep them under low watt lights? will prolonging planting them in containers hurt them?

i would go with something bigger for that long, but some people go all the way with party cups. rootbound plants grow slow and stay smaller.