LastModifiedTime property indicates the last time the activity was modified. This property is updated when the activity changes are committed via %XamScheduleDataManager.EndEdit(ActivityBase, bool)% method. The property's value is not updated as you set other properties on the activity.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2