Follicle size with ovadril trigger shot?

I had an ultrasound on Monday and had the follicules shown. Was told to trigger Saturday morning. Largest was a 12. I've heard people say it's bad to trigger follicules that are too small, obviously the RE expects them to grow. But it seems like a long time between when the ultrasound was done and when I'm triggering. Any thoughts or experience? This is also my first time doing the shot and I'm nervous!