It takes about 6-8 weeks for shoots to elongate. Needles fill out in summer and new buds are formed late summer/fall. If you're hand pinching the candles the time is after elongation and before the needles push out. They break off easily at that stage. When you pinch too early the shoots are soft and harder to remove so let them get some vigor before you pinch. One more thing is that all growing points do not emerge equally so I usually do all the most advanced shoots then visit again in the next few weeks until the tree is done.