I've been tray developing for 50 years and have never had perceivable fog from the timer display (which always seems extra bright just as the film back is opened) None the less, I still worry about light from all possible things and take precautions. I would blame age, but I have done this as a teen: When processing prints, I hate it when I reach for the timer switch and pull the inspection light switch instead, even though they are separated by a good bit.