The maximum time limit is the maximum amount of time a single algorithm is allowed to execute. The time limit is expressed in seconds. Click on OK to accept the modifications that you have made to the time limit. If you click on Cancel then all the modifications that you made to the time limit will be discarded and the time limit will not be modified.
If an algorithms exceeds the time limit, then you will asked either to abort or continue the algorithm with the Time Expiration dialog window. At that time you have also the option to set a new time limit.
For more information see:
Time Limit Expiration Dialog Window