The "correct" step to add cinnamon and vanilla?

I brewed a Cinnamon Porter two weeks ago. It just went into bottles.

I added two cinnamon sticks that were chopped in a food processor to primary fermentation. While primary was bubbling away, I put three more sticks into ~2oz whiskey (+ 2oz water) and swirled it daily for 4 days. This is a 5 gallon batch.

I put added the whiskey tincture into secondary for 4 days and the initial results have been promising. The aroma was there but not overpowering and the flavor was in the body of the beer but only if you look for it. I found this to be ideal. The flavor and aroma are there but not to the point that it smells like fireball whiskey.

Keep in mind that that cinnamon upsets yeast, so it may be best to just skip the 2 sticks in primary if you have a delicate beer to work with. I wasn't worried since mine was a porter.

If you're interested, send me a message and I'll update you when I try it on February 13th.

Best of luck!

EDIT/UPDATE: For future reference, the cinnamon aroma is definitely there in my porter though not overpowering. The flavor is there but not something to be in the forefront of the beer. I'd suggest skipping the cinnamon in primary (due to yeast interaction) and just make a whiskey tincture with ~3 sticks, crushed.

Haven't done anything with cinnamon, but have used a high quality vanilla extract (only alcohol extract, no sugars). I use some right at the end of the boil and another infusion in the secondary. I've had good luck with it and with the high alcohol nature, I didn't experience any issues putting it in the secondary.

Keep in mind a little goes a long way. If you use whole beans, make sure to open the pod, but you may want to put it in a hop bag so the vanilla bits don't get in the wort...unless you don't care about that. Good luck.

I use cinnamon sticks for a week in secondary fermentation to great effect. Lightly boil for 10 minutes in minimal water and add if you're worried about contamination. In a 5 gallon batch one stick adds a nice hint in an average ale but will be strong in anything light. Two sticks is for Christmas beer IMO.

Vanilla I've used in late boil and during secondary. Both are fine but for that nice smooth flavor I prefer to let them soak rather than boil them. Don't forget to cut the pod open so it will release that flavor.

Treat them like other additives (cardamom, rosehips,etc).

You can do either. I will add things at the end of the boil to impart more subtle flavor or if I want it to be more noticeable during the fermentation (similar to when people add oak).

I had good success adding a couple of cinnamon stocks during the fermentation. I would treat vanilla bean in almost the same manner.