Crossing event anytime during extended hours

I updated the title of the question to more clearly express what I believe you have requested. This should make it easier for other viewers searching for a similar solution to quickly locate this using the search function.

I think I understand the request but I'm not entirely sure. So I will restate this in my own terms.

You would like the scan to return a list of stocks that have had at least one positive MACD Histogram crossover at any time within the extended hours session. And you would like to be able to run that scan at any time during the current trading session. Which means for every stock that has a crossing event, lock that signal in and hold that for the rest of the current day's trading sessions.

This solution requires some extremely advanced code. Might seem simple to the average trader. But the code required to do this took me years to comprehend. (and even more time to learn how to compress it into just a handful of lines of code). Here is the solution I described above:

input regularSessionStartTime = 930;
input regularSessionEndTime = 1600;
def regularSessionHours = SecondsFromTime(regularSessionStartTime) >= 0 and SecondsTillTime(regularSessionEndTime) > 0;
def extendedSessionHours = !regularSessionHours;
def signal = MACDHistogramCrossover("crossing type" = "Negative to Positive");
rec trackSignal = if extendedSessionHours and regularSessionHours[1] then 0 else if extendedSessionHours and signal then 1 else trackSignal[1];
plot scan = trackSignal;