On the Actions menu, the Touch 
command modifies the timestamp (date/time last modified) of the selected files.
If Copy timestamps from other side is selected, then the timestamps of the selected files will be set to match those on the other side. If Set timestamps to --> is used, then any date/time can be selected from the calendar.
The Default selection controls how the calendar is initialized. Current system time will initialize the calendar to the current time. Last touch will recall the timestamp from the last touch operation. The Default selection only initializes the calendar -- you can still change it to any date or time.
If a folder is selected, the Touch command will attempt to change the folder's timestamp but not that of its contents. This command will fail if the operating system does not allow changing folder timestamps.