Which timestamp convention is most commonly used?

Timeseries data like weather data, user behaviour and simulation results can either be labeled at the beginning or the end of the interval. For example, the average zone tempearture between 14h15 and 14h20 can be labeled as 14h15 or 14h20.

What is the most commonly used convention in popular building simulation programs?

In DOE-2 and EnergyPlus, a day is from hour 1 to hour 24 and hour 1 presents the time interval 00:00:01AM to 1:00:00AM.

Source: Comparison of Building Energy Modeling Programs: Building Loads

Side note: It makes it a bit tricky to import it directly into programming languages such as Python (Pandas) in the case of E+ When you have varying reporting periods (in DOE-2 you know it's 8760 hours...)