How long do people see the "new mark" in a library on files? Or which criteria must be fullfilled that this mark will disappear?
The default setting for SharePoint 2013 is two days, which you can check using this script:
$WebApp = Get-SPWebApplication http://portal $WebApp.DaysToShowNewIndicator 2
You can change the number of days the same way:
$WebApp.DaysToShowNewIndicator = 5 $WebApp.DaysToShowNewIndicator 5
The !New icon will show by default for 2 days after the item is added. It can be modified to be longer or sorter.
stsadm.exe -o setproperty -pn days-to-show-new-icon -pv [number_of_days] -url [servername]