The best time to repot would probably be late winter/early spring when new growth is just about to burst. The lack of growth may be due to root developement, or it just isn't in one of its growth spurts. Give it time.

Pines generally only have one flush of growth per year. You may be able to see the buds forming that will make next years candles but otherwise you shouldn't see constant needle production. It's just not what they do.