Stig I am afraid this timer is not based on the number. When program runs scan for changes, it does not know yet how many files were changed/added/deleted in the folders. That is why it has to run this scan - to figure this out.
The only exception is initial indexing. In that case yes, program first runs quick scan to compute number of files and only then starts processing. All subsequent scans are done without prior file count (as this would basically double the time of the scan itself).
