When should I add my tincture?

So, "right before bottling" is kind of a relative phrase. I like to add stuff like citrus peel to the secondary about a week before bottling. Also, you said you soaked it in vodka. Save that liquid; it's essentially a homemade extract. If, after a week, there isn't enough grapefruit flavor for you, you can slowly mix that fruited vodka too your beer until you get to your desired flavor.

 

Are you bottling from bucket?

 

Add it right to the O2 purged keg before you rack your beer into it. Then you can purge out O2 again and shake the keg up to mix it well. Then carb.

I'd start with like 1/2 of what you think you should add and then dose up according to taste.

 

I make a beer with a mint tincture. I add it to the keg. Lets me start lower than I'll probably need and dose up. Keeps it from becoming too strong. Works great, just purge oxygen after opening to add more tincture.

 

I really like the idea of adding 1/2 as much as you think you want. Honestly, you can carb the beer without it altogether. Pour a pint and add a T of the vodka into the pint glass. Get it to your liking and multiply that by how many pints you have left in the keg. And then 1/2 that much. Double it later after you decide that @hoptualBrew and I are wrong. It's worth a little CO2 and fun to mad scientist to your liking.

I think I'm the only one on the forum who advocates adding flavor directly into the pint glass. No shame there.