Regular expression for matching HH:MM time format

Your original regular expression has flaws: it wouldn't match 04:00 for example.

This may work better:

^([0-1]?[0-9]|2[0-3]):[0-5][0-9]$

Regular Expressions for Time

• HH:MM 12-hour format, optional leading 0

    /^(0?[1-9]|1[0-2]):[0-5][0-9]$/
  

• HH:MM 12-hour format, optional leading 0, mandatory meridiems (AM/PM)

    /((1[0-2]|0?[1-9]):([0-5][0-9]) ?([AaPp][Mm]))/
  

• HH:MM 24-hour with leading 0

   /^(0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/
  

• HH:MM 24-hour format, optional leading 0

   /^([0-9]|0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/
  

• HH:MM:SS 24-hour format with leading 0

   /(?:[01]\d|2[0-3]):(?:[0-5]\d):(?:[0-5]\d)/
  

Reference and Demo

None of the above worked for me. In the end I used:

^([0-1]?[0-9]|2[0-3]):[0-5][0-9]$ (js engine)

Logic:

The first number (hours) is either: a number between 0 and 19 --> [0-1]?[0-9] (allowing single digit number)
or
a number between 20 - 23 --> 2[0-3]

the second number (minutes) is always a number between 00 and 59 --> [0-5][0-9] (not allowing a single digit)