You may not light Jewish festival (or Shabbat) candles before plag ha'mincha.  The candles must burn until at least dark (tzeit ha'kochavim) and someone must be there to see the light from the candles after dark.
SITUATION  Mincha minyan begins at plag ha'mincha. You cannot light candles at home and still get to mincha minyan on time.
WHAT TO DO You may light a candle without a blessing, just so you can have a flame for after the festival has begun. You go to synagogue and after ma'ariv you return home and light the candles from the flame which was burning from before sunset. If you will not have a flame burning from before sunset, you must say mincha on your own (anytime from half an hour after mid-day until sunset). You will light candles after plag ha'mincha but before sunset and not join the mincha minyan. Women should skip mincha and light candles either 18 minutes before sunset or have a flame burning from before sunset and light candles from that flame once the festival has begun (but she may not light from a new flame or a match).