This falls into the LoadTest category.
The issue is, how do you get N eValid copies to all start in unison.
The way we do this is to have all of the N eValid instances that you want to start in unison, have a synchronization command in the script that waits for a signal that YOU control, or waits until a specific time arrives.
To wait for a specific time requires rewriting the script if you want to change the start time, so that the script synchronizes on when a visible clock of some kind has a specific value. While that works OK, it is a lot more work than the alternative, described next.
The better way is to have all of the playbacks wait for a change in a known page, which change YOU control.
Here is a perfect example of a LoadTest Playback Synchronizatiobn Page
that does just this. Enjoy!