Translations:Using regular expressions/115/vi
From LimeSurvey Manual
/^(?:(?:00:[0-5][0-9]:[0-5][0-9] (?:am|AM)|(?:0[1-9]|1 [01]):[0-5][0-9]:[0-5][0-9] (?:[ap]m|[AP]M)|12:[0-5][0- 9]:[0-5][0-9] (?:pm|PM))|(?:[01][0-9]|2[0-3]):[0-5][0- 9]:[0-5][0-9])$/