How long does the egg 'get ready' for before actually being released?

I had a transvaginal scan 4 days ago and she showed me the follicle getting ready to release an egg on my right side. I started testing for ovulation twice a day 12 hours a part a day after my scan but I haven't had a positive yet. I have long cycles so I'm not meant to be ovulating just yet anyway. Should be ovulating at the end of the week which will be exactly a week after my scan.. So does the egg take a week or something to get ready to be released? Is this normal?