I can't see why you've posted this to the LCL part of the forum.
You'll find the runtime library described at
https://www.freepascal.org/docs.html , including RTL -> DateUtils.
However if you are confident that you know that the format will always be hh:mm (or perhaps hh.dd for the "dismal hours" beloved by American corporates) you might find it more efficient to parse the input yourself to minutes or seconds relative to some arbitrary datum.
I'd throw in that I think there's an important point to be learnt from (SQL) databases here: hh:mm can either represent a time or an interval. You can add a time and an interval (giving you another time), you can add two intervals (giving you another interval), but you can't add two times.
Taking that into account, a time needs a datum and you need to consider what you do if it exceeds 24 hours, while an interval doesn't need a datum and can exceed 24 hours.
MarkMLl