I agree, pick a method and stick with it. It doesn't matter if you start pouring 20-30 seconds early or right at the time, or pour early enough to start or finish pouring in the stop.(posted 8584 days ago)BTW when do you start timing, when you start pouring in the developer? Or after it is all in?
Again, as long as you do it the same way every time you will be fine.
Realize that the published times for B&W developing are recommended starting points. They are not exact nor will the work for everyone. You will have to adjust things to make them work right for you.
This is why it is commonly suggested to use only 1 film and 1 developer for at least a year. That way you learn that combo and figure out how to make it work. It also gives you the experience to quickly adjust to a new film or developer.