There is no fixed answer for this question. The length of time it will take for a scenario to start running after the user clicks the 'RUN' button or sends remote commands to start the scenario will depend on the following:-
In general, basic use of a scenario will mean it is loaded and run manually. This means that the user will click the 'RUN' button in the GUI to start the test. When the RUN button is used the software actually performs an ARM sequence, which initialises all the channels on all the simulators which will be used in the scenario, before running the scenario. Since every scenario may require a different number of simulator channels to be used and different customer systems may involve different simulators there is no simple answer to the question "how long does a scenario take to start running?". It can be anything from ~3s for a simple GPS only scenario using a GSS6700 to ~30s for a multi-constellation scenario using 2 or more GSS8000's.
The most appropriate way to control the start of the scenario is to send the remote ARm command first. This then takes care of the simulator channel initialisation sequence BEFORE the scenario starts running. Let us take the example of using the DISABLED trigger mode (default trigger state):-
Some users however simply become familiar with their system and know approximately how long a particular scenario configuration will take to start running. This is acceptable as long as they have no need for precise timing between starting the scenario and the scenario actually running.
Higher precision control requires better remote control of the start of the scenario, being able to monitor the simulator 1PPS or using external triggering. To learn more about trigger modes please refer to article SOL10180 or the SimREMOTE manual DGP00792AAA.