You should brush, 20-30 minutes after eating on the night (just before you sleep) and, 10-20 minutes before eating your breakfast. Midday brushing, is not essential for most albeit, it’s highly dependent on your dietary habits. The same rule applies: 20-30 minutes after eating or 10-20 minutes before eating. The time-rule is influenced/is-in-place to compensate for the time it takes for the normalization of the oral PH after food consumption (“after a meal”), and the latter being to ensure that the introduction of food stuffs and liquids will not diminish the concentration of the essential fluoride, contained within toothpaste, on the tooth surface