This is a tough one. Many a cutting has been lost due to an eager gardener checking for roots. New growth on the cutting does not necessarily mean that the cutting has rooted. Cuttings can put out new growth and even attempt to bloom, before rooting. The only way to know for sure is to see some roots, or feel some resistance from roots in the soil.

One thing you can do is put the cutting into a clear container to root, such as a baggie, a clear storage tray, or a clear plastic cup. This makes it easy for you to pick up the container carefully and look on the bottom for roots.

If this isn't possible, you can gently tug on the cutting, and if there is any resistance, you can assume there are roots. Do this very carefully, as these new roots will be very fragile and easily snapped or broken.

If you are working with sand, it is possible to very carefully "dig up" the cutting to see if there are roots or callous. The sand should allow the cutting to slip out with some ruffling from you, and the cutting can be slipped back into the sand after inspection. Be extremely careful in doing this. It is all too easy for the roots to remain in the sand and the cutting to come out, and how disappointing that can be!