The time of a simulation in your scripts is determined by two variables: $start_simulation and $end_simulation, which can be set up in the "Define simulation parameters" section. These values determine for how long packets will be sent and received in your simulated network.

The time of statistics collection is usually shorter that your simulation time; certainly, it cannot be longer, otherwise you'd be collecting data related to events that are NOT taking place. Usually, you should be able to identify a "transient" and a "steady state". The "transient" is an interval of time during which the dynamics of the simulated system are still "warming up", and therefore the measured quantities may not be representative of the actual system performance (i.e., the initial slow start of a TCP connection). The "steady state" is the interval of time when the behavior of system should approximate the behavior that a casual observer expects (i.e., in the case of TCP, a repeated pattern of slow start followed by congestion avoidance, then again slow start and so on). Depending on your needs you may want to collect statistics during the steady-state period only, or to examine what happens during the transient as well. The time when statistics collection begins is set by the variable $start_stats, and collection end is set by $end_stats