Never should one paint "wet on wet" for sure. My guess is industry standard is to follow the manufacturers recommendations for dry times. They also recommend the proper cleaning/prep methods, primers, application method, wet/dry mills, a.k.a "coating system"....If you offer your customers a warranty and don't want to be stuck holding the ball on the whole deal, or you want to guarantee consistency and quality, I recommend following what the mfg. says in order to hold them to thier warranties as well. It's also hard for the homeowner to argue about what they need when you are holding data sheets or the current coating systems catalog from the mfg in your hand. For instance: This is Duration Home Interior Latex Matte that I use frequently.
Drying Time, @ 77°F, 50% RH:
temperature and humidity dependent
Touch: 1 hour
Recoat: 4 hours
Just a side note. I almost never have to cross hatch north south east west any walls. I only roll a different direction when the roller doesn't fit or if there is a low spot in the wall the roller refuses to paint...If you use enough paint and let the roller apply it properly instead of trying to spread paint, you can paint one to one and a half strips straight up and down all the way down the wall and not have any issues with flashing or coverage. Use LOTS of paint when you roll...SMOOTH, semi-gloss ceiligns and things of that nature are sometimes obviously a different story.