You definitely still need to be sure that you're night cycle isn't being disrupted during flowering. The plants have a biological mechanism that kicks in when the nights are at least however long depending on the strain. In darkness a growth hormone builds up until the sun comes out and destroys it. Once the nights are long enough for the hormone to reach the level for your particular strain for a few consecutive nights they'll start flowering. Even if the street light is on a timer the plant won't be able to adapt to it. Your plant is obviously already flowering but the light can also make them take longer to finish and keep them from ever putting all of their energy into it affecting yield and quality.