Hello @WesselHL , and welcome to the KNIME community.
You can test with ‘Column Expressions’ node (Type == Local Time / String):
hours = padLeft(floor(column("time_sec")/3600), 2, "0")
minutes = padLeft(floor(mod(column("time_sec")/3600, 1)*60), 2, "0")
seconds = padLeft(mod(column("time_sec"),60), 2, "0")
join(
hours
, ":"
, minutes
, ":"
, seconds
)
BR