This is the reference and an online converter.
The 18-digit Active Directory timestamps, also named ‘Windows NT time format’,’Win32 FILETIME or SYSTEMTIME’ or NTFS file time. These are used in Microsoft Active Directory for pwdLastSet, accountExpires, LastLogon, LastLogonTimestamp and LastPwdSet. The timestamp is the number of 100-nanoseconds intervals (1 nanosecond = one billionth of a second) since Jan 1, 1601 UTC.
Other converters
Microsoft Windows
In Windows (command line) use:
w32tm.exe /ntte 131001091660000000
PowerShell
(Get-Date 1/1/1601).AddDays(131001091660000000/864000000000)