When can one prune an aerial root on a Shimpaku Juniper?

Hello!
I have a small aerial root growing close to the base of my shimpaku juniper.
It is about 3mm in thickness.
I am not repotting the plant this year, but I wanted to ask what time of year is best to prune aerial roots on shimpakus which have thickened over the winter. I do not want to leave the root to continue thickening, but I also do not want to harm the tree by pruning the root too early or too late in the growth season.
Any insight would be appreciated!
KH

Junipers do not have aerial roots.

I'd guess you can cut a 3mm root without problem. Don't know / can't see the tree though.

Thank you!
To clarify, when I got the tree last year, it was in rough shape and dense moss had surrounded the base of the tree above the roots.
When I cleaned up the tree and removed the moss, the 'aerial' root had been growing within the moss and above the true base and nebari before entering into the soil.
As such, there is a root which has thickened and sits above the actual base of the tree.

If the plant is healthy and you do not have a 5mm trunk on this plant, but a substantial trunk you can cut a 3mm root any time you want.