SPFile.CheckedOutDate property
SharePoint 2013
Gets the date and time that the file was checked out.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
Property value
Type: System.DateTimeA DateTime object that specifies when the file was checked out in Coordinated Universal Time (Greenwich Mean Time).
The CheckedOutDate property throws an exception if the CheckOutType property contains SPCheckOutType.None.
A locked document is always checked out.