For me it was about 1 week when I figured I might have a problem. Prior to that I just blamed it on crappy gear with too much solvent and figured it would take care of itself. It had been painful, swollen some, and reddish but no more than other times I had done similar injections.
I waited about anothecr 5 days because I felt it would clear up on it's own and I didn't want to tell a doctor I had been injecting steroids.
By that time, almost 2 weeks after injection I developed a fever and signs of an infection such as the spot was hot to the touch and the skin had a bumpy appearance. There's a name for that but I forget.
Urgent care drained the abscess and prescribed antibiotics. Also gave me IV antibiotics to get me started. About 1 month or more treatment on many antibiotics proved futile in getting the abscess to heal. The hole wouldn't heal. When you have this you have to keep packing the hole with gauze. Its nasty. Finally had surgery to debride the area and sew it up. It was fine after that.