Think about McDonald. Would you want to wait 15 minutes in the drive-thru for a number 1? No, the first time it happens you may brush it off as an anomaly but if it happened two or more times, you would probably stop going there.
You can also think of wait-time in terms of a manufactured product or a production line. Waiting for a process to complete while idle is costly to any organization. Wait-time must be minimized at all cost.
What ways can you ensure that the level of benchmarking (wait-time) is consistent with the expected value of the BPO? (Try to answer this question as though you were both the vendor as well as the client.)