You can calculate the number of instances in the summary by using a calculated field in the table that only has 1 as its formula and totalling this for the operator with a sum formula in the summary. Then you should be able to use that field to calculate the average as you have already tried, thereby avoiding having to use the count field. You can hide the new table field if you need to.
When working with times, especially when doing more than time difference calculation and even then being careful, it is best to convert you values to seconds, sum the number of seconds, calculate the average and then convert back to a time format - probably HH:MM:SS in most but not all cases.
It's not easy to be sure of what you are dealing with from the information provided.
Is the Time value of 18886 in minutes?
Looks like it might be.
On the other hand your formula refers to a field by a name that suggests ITS value is in hours and minutes. It may not be in hours and minutes but it would be good to check.