Manual dosing can be acceptable, but isn't best because it causes fairly large swings in your salinity, pH, and your Ca/Alk. I belive Randy said in "What your grandmother never told you about limewater" that up to 1% of your tank's volume may be acceptable to dose at once, based on perameter swings. Though this is harder for your tank to acclimate. Generally people seem to notice that their coral start growing much faster when they get their perameters stable, and doing 1 daily dose doesn't meet that.
If you have time, it's best to space your daily dose out into as many smaller increments as convenient throughout the day.