So, I've added my grapefruit potion along with my hops in the secondary fermenter. Will it need to stay in the secondary fermenter longer because of the added alcohol / ingredients?
Only if there were more fermentables added from the "potion", i.e. fruit juice or other sugars.
First you have to know that airlock is not for detect if fermenting or not. Airlock function is to leave co2 out and air not, for testing if is fermenting or not you have to mesure density.
Always you add something external you have to check if it is fermentable ( fruit, sugar, honey) if you dont know better to give some time ( 1 or 2 days ) so the sugar on this products become soluble in beer, then to give a density reading.
Wait 1-2 weeks and then make another reading. After that reading if you see diferences make 3 consecutive readings within 1 day each one.
If you get 3 readings same the fermentation its over, go cold crash - bottle - drink as usual!
if you get diferent readings, it still fermentation. Wait another week and repeat.
Sry for my english.
Hope it helps you!