Rare Bosnian Pine (Pre Bonsai) 3 Gallon

Shortening (pinching) candles is more of a silhouette confinement (refinement stage) technique and not necessarily used to accelerate the formation of interior budding / density.

If you want interior budding on your branches, then keep them vigorous and strong while lowering them down with wire to allow light to penetrate into those interior regions.

You want to wait till interior buds form and then open into shoots, and then have those shoots be strong enough on their own (sap flow wise) before either A) shortening those branches to those shoots or B) using silhouette/refinement techniques (pinching).

But all of this is putting the pine cart before the pine horse, because your pine is still in what looks to be dense organic nursery