I'm a little surprised nobody on this site could help when I assumed it would be THE place for MetaTraders solutions. Anyhow, just in case someone in the future ends up here looking for what I was looking for, the following code does the job of defining the time specific start and end points for the high and low.

xdt_to = StrToTime(StringConcatenate(TimeToStr(iTime(Symbol (), PERIOD_D1, 0),TIME_DATE), " 01:00"));
xdt_from = StrToTime(StringConcatenate(TimeToStr(iTime(Symbol (), PERIOD_D1, 1),TIME_DATE), " 23:00"));