Quoting from your first post: "If I where to input in a cell 488 I would like to see in another cell 08:08, is this feasable?"
If you input in cell B2 488 you will see in cell C2 08:08. It is feasible and the formula for cell C2 is =DURATION(,,,B2). Some formatting of cell C2 is required to display the result in the exact format you are requesting.
If you would, instead, like to type 488 into a cell and have it reformat into 08:08 in the same cell, first use the formatting sidebar on the right to format the cell as a duration with the units hours and minutes and displayed as 00:00. When entering the 488, put a "m" on the end so it knows it is minutes. 488m