I'm trying to air layer my Japanese Maple tree and I want to check for roots. However, the person that helped me used black duck tape around the bag, so taking the tape off will tear the bag. FYI, please don't let the camera distract anyone.
The quickest way to mess up an air layer is to check the roots. Leave it alone until it's time to separate. Aroynd here, layers are separated at the end of summer. At that time, the roots will be thicker and a little more resilient, but still pretty tender.
Where are you located (generally)? If you're in a temperate climate with real winters you want to separate in time to give your new tree some time before winter. I always tried to separate at least six weeks before the anticipated first hard frost. As unpredictable as the weather is getting these days that can be hard to anticipate.
In my climate, we have what might be called a second growth period when the weather cools from the summer highs. This lasts from about early September through October. After the layer is separated, the roots aren't messed with at all, just placed into a pot. This gives the roots a chance to harden off before winter because the new roots (especially if done in plastic) are especially tender.