Can I write off meal expenses on stand-up (high-speed or continuous duty) overnights?

Yes.  A high-speed overnight (also called a stand-up or continuous duty overnight) is treated just like a normal two-day trip.  The reason that a high-speed overnight is deductible, while a day trip with multiple legs is not is because there is a rest period on the high-speed overnight.  During a day trip, the time between turns is not considered a rest period, but the time (although shortened) during a high-speed overnight does qualify.