The reason most people enter a parking space gong forwards is so that they can open their trunk and put the grocery bags in easily - to reverse in makes that very difficult. So, back ur carefully, take as long as you need and the rest of us will wait. It probably takes most people less time to back out than to back in anyway. Using a parking lot is a matter of polite give and take between all of us - forget "rules" and just do what works and we will get along fine.