Calculate and represent concurrent events

When having a table with start datetime and end datetime (second-granularity) is impossible to count concurrent events. As a workaround one has to build a calendar table with a crossjoin for every second in each day, and then a calculated column with concurrent eventsfor each second and the RAM blows up.
The problem is also with the visuals: when using a timeline on the x axis the value is expected to be displayed on a punctual time of the timeline, the concept of duration (e.g. a sort of gantt chart) is not managed.
DAX function are also weak on the datetime side, there are a lot of date function, less on time, and less again on datetime.