Please, define better what do you mean by "to run test list as fast as possible across multiple agents".
By design when the one schedule a test list to be executed on multiple machines - at the moment they start to run the scheduling server distributes the tasks among the execution agents. There is always few seconds delay before the test visual start of the execution, though.
Are there any related to this case exceptions in the application log? When you restart the scheduling service is this issue reproducible? What is your configuration setup - where are installed the scheduling, storage and execution servers?
I hope to hear from you soon.
Telerik by Progress