I prefer to transplant out of a seed mix as early as possible, so I would go ahead now. I don't think you will have enough mix clinging to the roots to make any difference, so would not try and remove it and risk damaging delicate roots. Al

I doubt anyone will want the cantaloupe, I know they are to late to grow up north, but I don't know about south.

If you have roots coming out the bottom of your "cells", I would transplant them now and begin a regular fertilizing regimen. I suppose you understand that grown from seed your trees may need 7 or 8 or more years to produce fruit; and the cultivar that you get will likely not be the same as you planted. Personally, if I were going to invest my years and energy, I would start with a grafted tree of the variety I liked best... Oro blanco seems to be popular at the moment; I have 3 at my lemon farm and it is the only grapefruit I would bother to grow.

OK, Here is the interesting thing about citrus. Citrus can be poly-embryonic. What this means is that from a single seed you can get 2 or more trees, (there are other plants that exhibit this trait, but citrus are well known for this tendency); the really cool thing is, with citrus, the resulting seedlings from the seed can be either of the following: 1. Exactly the same plant as the tree that produced the fruit. OR 2. A hybrid between the tree that produced the fruit and whatever citrus happened to pollinate the flower that produced said fruit. And since many, if not most citrus are self fertile, there is a pretty good chance that the seedling you have will be exactly like the tree that produced the fruit you purchased at the market. With this said, the issues with raising most fruit trees from seed is that you'll have to wait several years before you really find out if the resultant tree will produce fruit that is good. But as long as you are patient, and willing to baby the young tree through drought, winter freezes, insect pests and other adversities, you may have a real winner on your hands. Remember that MOST commercial fruit currently being produced originated as a cross between two open pollinated plants that were either different cultivars of the same species or very closely related species in the same family or genus, (citrus example: the grapefruit, a natural hybrid between the pomelo, (or shaddock) and a sweet orange). good luck!!!