Many people call that phlox but what you are describing is really probably commonly called "Dame's Rocket". The botanical name is Hesperis matronalis. (see link below)

The bloom time will vary from year to year depending on weather conditions, and plants grown in sun will usually bloom sooner than those in shaded areas. You're considerably further south than me, and your growing conditions (woods) is different from mine, so I'd hesitate to guess for you.

Here is a link that might be useful: Dame's Rocket