If you intend to eat your fruit straightaway, it is usually best to harvest it when it is fully-ripe. Fruits for storage should be picked earlier, when they are mature but not yet completely ripe. As most fruits ripen over a period of time, harvesting should also take place over a similar timescale.
The following table shows the harvesting times for apples and pears, and the defects in flavour or texture that may be caused by early or late picking: