Time Formatting (Number Format?)

Hello,

I've stumbled across a task I need a assistance with I was hoping someone could kindly assist me.

I have a column of data with hourly time in each cell stored in fractional format.

For example: 1 Hour and 15 minutes is stored as 1.25. Half an hour (30 Minutes) is stored as 0.5.

I have thousands of rows of data in this column that I need to format from 1.25 to 01:30.
I don't want to tamper with the data in the cells by dividing by 24 and then changing the number format. This is for marketing purposes and the data cannot be changed, nor hidden rows and all of that mess.
I am looking for a way to apply some kind of number format or conditional format that automatically changes this entire column, so if I were to enter 0.5 in a cell, it would automatically become 00:30, ect.

I've attached a dummy spreadsheet for your reference.

Thanks!