An answer I have test for my working hours tab

A short formula that I use and put the hours format automatically is

=TEXT(INT(A1) + (A1 - INT(A1)) * 100 / 60, "[hh]:mm:ss")

• INT(A1) take the entier part
• (A1-INT(A1))*100/60 convert the decimal part
• "[hh]:mm:ss" put the correct format of cell