Here is the code:
input startTime = 400;
input endTime = 929;
def timeUntilClose = SecondsTillTime(endTime);
def timeUntilOpen = SecondsTillTime(startTime);
def targetPeriod = timeUntilClose > 0;
rec targetPeriodHigh = if targetPeriod and !targetPeriod[1] then high else if targetPeriod and high > targetPeriodHigh[1] then high else targetPeriodHigh[1];
rec targetPeriodLow = if targetPeriod and !targetPeriod[1] then low else if targetPeriod and low < targetPeriodLow[1] and low > 0 then low else targetPeriodLow[1];
AddLabel(yes, Concat("Period High: ", targetPeriodHigh), Color.GREEN);
AddLabel(yes, Concat("Period Low: ", targetPeriodLow), Color.RED);
Screenshot below shows the result.
User inputs allows to change the target period. If you try to set the time in a way that spans two dates the code will fail.
Is that actually CL or did you mean /CL? This is not intended for futures, only stocks. As to the plot lines. I never included those in the chart as the request was for chart labels only. The lines you see on my screenshot were hand drawn and only included to show the labels are displaying the correct value.