AFAI understand the script it takes, as DetlevD states
the VBS script should return a valid result as
is filled.
Who fills that field? I think that would be you, the user. So you have all the options to adapt any input to match the required format. And once you have adapted the contents of LAST_FILE_MOD_DATETIME the existing script should work.
Which means: you have to take care about the daylight saving times and add or subtract 1 hour. Also you have to remove any "T" or trailing letters.
And all this could achieved with actions that you execute prior to calling the VBS script