By default Oracle DAC allows to execute just 1 execution plan at the same time.
As long as the executions plans are not dependent each other ( using same tables) is possible to run more than 1 execution plan at the same time.
DAC–> Setup –>DAC System Properties –> Concurreny Label:
Change the default value 1, to the desired number of parallel executions plans.
Important:
To run at the same time, make sure the Execution plans dont have common tables.
Oracle OBIEE 