[Solved] Calculate total playing time of files

We have a project (digitalization of thousends tapes) with 16.400 WAV files 96kHz 24bit (8.000 GB) and would like to calculate the total playing time. (To bill the customer)
Unfortunately, this can not be determined correctly on the basis of the file size.
We had tested with a few files, that have 1 hour playing time, but nethertheless different file size (for whatever reason).
For a few years Wavelab 5 or 6 (?) showed the “total playing time” within batch processes - but this comfort was left out in version 9 and 10.

So do you know any app, that can sum up the total playing time with 96/24 files?
Or is it possible to calculate this in WavLab ?

VLC-Media-Player can calculate a complete Harddisc with only one drop and drag.
Just dropping the customer folder with all subfolders to the playlist.