Turtleneck Shrug Sleeves?

So I'm nearing the end of my first sleeve in the turtleneck shrug. I'm just about up to the armpit, and it's only 18". I remember some of you mentioning that the sleeves were a bit too long for you, but at what point in the knitting should I start the top shaping?
I'm thinking, knit to the pit, then do the CO15 and knit up the shoulder? Does this sound right for those of you who've already done this? Any advice (for this or beyond)would be appreciated! Thanks!

PS: this is Patons Classic Merino in "tree bark mix". Fairly soft and nice and thick. (and much, much less expensive than using Rowan Kid Classic, although I'd like to have!)