concatenate(
right("000" & floor([Time_Remaining]), 3),
":",
right("00" & number(([Time_Remaining] - floor([Time_Remaining])) * 60), 2),
":00"
)
If you take two numbers (miles) and (miles per hour) and divide those two, it will give you a decimal.
To convert that decimal result into a duration, it requires a little slicing/and/dicing of the decimal.