To quote the line on Simulation Control sub heading “The end time, ’15 s’ is the time in which you want the simulation to run, and the maximum run time, ‘3e+6 s’ will cap the simulation to the maximum time in real-time.”
Can you please confirm me whether my understanding is correct,
15 seconds = Means the Physical time (in the real world)
3e+6 s = Is the CFD run time
Hey @vigneshn!
Maximum run time: This value is like an upper bound meaning that after this time has passed, the simulation will be canceled. The solver also considers that the simulation might take this much time to be executed, and given that your quota is insufficient, an error will pop up.
As for the end time, I would like to refer you to this documentation page as you should read for the FEA & CFD solver depending on what you want to use to get a better understanding of all the settings (better than me copy & pasting it here) 
Hope that helps!
Jousef