How much time is between a new moon and a full moon phase?

The full moon cycle (from one phase to the same phase again), from start to finish, is generally 28 days. That being said, from one phase to its opposite, or one half-cycle, would be approximately 14 days.

A lunar month consists of 28 days, during which each phase of the Moon is visible. The time between New Moon (dark) and Full Moon is 14 days : approximately 7 days from New Moon to First Quarter and 7 more from First Quarter to Full. Similarly, it is 7 days from Full Moon to Last Quarter and 7 more back down to New Moon. The time between consecutive appearances of the identical phase is always 28 days.