Excel question calculating an average turn around time

I have a cvs report that calculates a turn around time from when a report was dictated to when it was transcribed. I drop this report into Excel so that I can then calculate the average TAT of all reports. My trouble comes when the TAT is greater than 24 hours. The data comes in the format d hh:mm:ss (for example 1 02:11:01). I have tried applying a custom format with d:hh:mm:ss and also d.hh.mm.ss. Everything I try completely ignores the day when doing the calculation.