AsianH = ValueWhen(TimeNum()== 073000,HHV(H,TP) ); // TP is the lookback period
This says that when time equals 07:30 then find the highest value in 
last "x" amount of bars. I use an TP = 
IIf(Interval() == 1800,8....etc statement to change the lookback depending on the current 
chart interval.
Where it falls over is 
if the current chart interval is say hourly. Then the TimeNum()== 073000 is never true. So how to I access "TimeNum()== 073000" 
on an hourly chart so I can plot a line 
showing the session high/low? Thanks.