Getting Premarket Prices (during the day)

[Rla1js]

At any time during the day, how would I get the open price at 6:00am -- assuming my time template includes that time and regardless of the chart interval?

Once the regular session starts, I use open(0,inv("D") to get the opening price -- but I can't seem to find out how to get an opening price at other times in premarket.

Thanks.