Time validation from validation.xml file

Question

i've inherited part of a project and need to be able to validate a user inputting time into a field, at present it's set for a 24 hr clock, but the mask as it is will let them input eg 25:45, because its checking each digit rather than is it less than 24
entry from our validation.xml file:
<field property="time" indexedListProperty="configBillingPeriodTable" depends="mask">
<arg0 key="taWebLabel.Time"/>
<var>
<var-name>mask</var-name>
<var-value>^[0-2][0-9]:[0-5][0-9]$</var-value>
</var>
</field>
this stuff is new to me, so excuse the basic questions!! how can I set the first part of the mask to limit to 23, and where can I find info on what expressions I can use between the <var-value></var-value> tags
thnx

Answer 1

I believe it would be this:
^([0-1][0-9]|[2][0-3]):[0-5][0-9]$
or if you don't want leading 0's for 0-9...
^([0-9]|[1][0-9]|[2][0-3]):[0-5][0-9]$