[Timelime] Total time for overlapping tasks

I am sometimes working at different tasks at the same time, for example, when writing a document while running a simulation in the background. It seems to me that the total time in the pie and bar representations is just the mere sum of the single times of each tasks: if I run a simulation from 8 to 9 and write the document from 8 to 10, the total time will be set to 3 hours instead to a more reasonable 2 (from 8 to 9 I have worked on two tasks but there is no need to count it as two hours!)… any solution?