I'm pretty sure you can take cuttings from an actively growing tree and root them immediately. They do not need to be dormant and they don't need a "chilling" period in the fridge. If you root them now, you do have to keep in mind that they will still be very small at the end of the season and may need extra protection if winters are cold where you live.
If it were me, I would air layer them. You'll have 4 healthy plants a lot faster than you would by rooting the cuttings. Also, depending on your skill in rooting cuttings, you will probably have a higher success rate with air layers than you would with cuttings, so you might end up with the same number of trees in the end anyway.