I find that if I use a dilution on my film developer that gives me a little extra development time it is much easier to get exact times. On 8 minutes of dev. time an extra 30 seconds is negligible. If you are using a concentration that says 3 min. dev. time 30 sec. extra has a big difference. Slow has many advantages. I also use another film tank holding the precise amount I will need so there is no doubt the tank is full.