In number one the amount of billable seconds saved for a one second phone call is the same as a 61 second phone call, 121 seconds, 181 seconds…
In number two the amount of billable seconds saved for a one second phone call is different than a 61 second phone call, 121 seconds, 181 seconds… so the average will be different. However the longer the phone call the closer the average will be to 27.0. After 10,000 seconds the average is 27.0032, after 20,000 seconds the average is 27.0018. Keep going towards infinity and the limiting average is 27.0 (although it will never hit 27.0).