plot when stock quickly drops 15 percent from high

The screenshot you sent me via email does not fit the specifications you listed in your question above. The 15% drop occurred 17 bars from the high of the day. I have provided user inputs to your study so that the percent values can be adjusted as well as the number of bars from the high. In a 1 min chart your signal occurs 17 minutes after the high of day was reached. I used an arrow instead of a dot because the dot did not show up well on the chart.

Here is the code. Screenshot below shows the result.

Edit: Sorry but I was in a rush to get this posted and neglected to ensure all the rules I had accounted for in the code were applied correctly. The code below has been updated to ensure correct operation.

input percentGain = 30.0;
input percentDrop = 15.0;
input dropWithinBars = 10;
def previousDayClose = close(period = AggregationPeriod.DAY)[1];
def extendedSessionOne = RegularTradingEnd(GetYYYYMMDD()) <= GetTime(); def extendedSessionTwo = RegularTradingStart(GetYYYYMMDD()) >= GetTime();
def extendedSessionHours = extendedSessionTwo or extendedSessionOne;
def regularSessionHours = RegularTradingStart(GetYYYYMMDD()) <= GetTime() and !extendedSessionOne; rec highOfDay = if extendedSessionHours and !extendedSessionHours[1] then high else if high > highOfDay[1] then high else highOfDay[1];
plot highForToday = highOfDay;
def highEnough = highOfDay >= previousDayClose * (1 + (percentGain * 0.01));
def lowEnough = low <= highOfDay * (1 - (percentDrop * 0.01));
def highestBarOfDay = high < highOfDay and high[1] == highOfDay[1];
plot signal = highEnough and lowEnough and !lowEnough[1] and Highest(highestBarOfDay, dropWithinBars - 1) > 0;
signal.SetPaintingStrategy(PaintingStrategy.BOOLEAN_ARROW_UP);
signal.SetLineWeight(4);