You have to extract the hour, minute, and second substrings first (e.g. using
MID()
) and convert them to double.
How to create the final double value depends on what it should represent:
dblSeconds = hr * 3600 + min * 60 + sec
dblMinutes = hr * 60 + min + sec / 60
dblHours = hr + min / 60 + sec / 3600