I’ve not been able to find the ‘allowed’ or permitted possible time patterns and attempting to use the ‘HH:MM:SS’ format is not giving me the leading zero.
Unlike the datepattern( function, timepattern( makes no distinction between upper and lower case. MM and mm will both give you two digit minutes, SS and ss will both give you two digit seconds. HH and hh will both give you one or two digits as needed, with no leading zero. You are just going to have to use
("0"+timepattern(time,"hh:mm:ss"))[-8,-1] if you need that leading zero.