QS:Date time format
From LimeSurvey Manual
Date/Time format
Description
This question attribute can be used to specify a custom date format. If it's empty, the survey date format is used.
Valid values
The d/dd m/mm yy/yyyy H/HH M/MM formats and "-./:" characters are allowed for day/month/year/hour/minutes without or with leading zero respectively. Example are: "yyyy-mm-dd", "dd.mm.yyyy HH:MM", "HH:MM"