This solution will only work if you have included extended trading hours on your chart. I have included user input to allow adjustments to the regular session start time as well as the moving average elements.
input sessionStartTime = 930;
input maLengthOne = 10;
input maTypeOne = AverageType.EXPONENTIAL;
input maPriceOne = close;
plot maOne = MovingAverage(maTypeOne, maPriceOne, maLengthOne);
def newDay = GetDay() <> GetDay()[1];
rec pmAverage = if newDay then maOne else pmAverage[1];
rec regAverage = if SecondsFromTime(sessionStartTime) == 0 then maOne else regAverage[1];
AddLabel(yes, Concat("PM Avg: ", Round(pmAverage, 2)), Color.WHITE);
AddLabel(yes, Concat("Reg Avg: ", Round(regAverage, 2)), Color.GRAY);