I've gone one day early or late. The only problem I had was when I was injecting biweekly and trying to move my shot date later. My T level was troughing as it was, so I was feeling depressed and lethargic. Waiting a day was hard. It's all I thought about!
If you're injecting weekly, you probably won't notice any real difference. Every two weeks? It depends on you.
But I'm not a doctor, of course.