How to calculate mean call rate

Hi I have a script that I have written to solve a problem for an assignment. I was wondering if I could get help on this? I have to write a Matlab script that calculates the mean call rate for animal IDs 1, 2, and 3 (ignore 0) for the entire session (e.g. no. of vocalizations/minute). For session duration, i can use the last value of the audiostop time column. The entire dataset (LabelTable.mat) is a continous recording of three indviduals. So to get mean call rate (number of vocalizations/minute) I would need to include the total duration of the experiment. Total duration of the session in minutes is given by the last value in the Audio Stop Column: 2.019e+04. I know how to calculate the mean (mn1 = mean(Animal_ID_1.AudioStopTime-Animal_ID_1.AudioStartTime), but what im confused about is how incorporate value of the total session duration within the code for the mean?

I have provided the sample data: LabelTable.mat