sum of value of duration field for multiple records should not be more than `n` minutes.

Hey,
I'm working on a use case where I created a section 'Concert'. When I open any concert record It has some records related to 'Performance Detail'

Now I have to perform validation on PF_Duration Column. The Query is following:
"Perform verification whenever user adds or modifies a performance as follows: if the total duration of the concert performances exceeds the system setting value (see above), saving a performance record should not be permitted. Instead, a user should receive a message informing that no more than “N” total performances duration is allowed. “N” is the system setting value." 
N = 150 minutes