Resolution: Elapsed time of an activity is the time difference between start and end time of that activity. Between the start and end time, control may get switched with other activities from other jobs.
If your concern is to find the bottleneck, you can use the statistic collection feature in Admin and look at the "Eval times" of the activities. The activities with the highest eval times are the ones affected.
Eval time -- This is actual time taken to execute an activity.
Elapsed time -- This is the time taken to execute an activity plus all the delays in acquiring resources like engine threads, JDBC connections, network, etc. Many times a higher elapsed time ( but ok eval time) means incorrect engine tuning or a bad design in the process. This would mean the engine is starving for threads. If there are no real activities which are taking high EVAL times, it is a matter of tuning the BW engine with the proper values of MaxJobs/ThreadCount/ActivationLimit.