You'll need a combination of Equation Fields and a Text formula field with regular expressions to make this work. Let's use 10.24 hrs as an example.

1) Create fields for DECIMAL TIME(Number), HOURS(Equation), MINUTES(Equation), and SECONDS(Equation)

*This sets up our variables for making the time readout*

2) Set all fields except for DECIMAL TIME to 'Round Down' from the Rounding pulldown menu and '0' in Decimal Places

*This will give us the absolute values for Hour, Minute, and Second variables*

3) For all fields except DECIMAL TIME and HOURS set 'Format' to Custom with the value 0 in 'Before'

*This is to generate two digits for every time value*

5) Equation for HOURS should simply read {DECIMAL TIME}

*For a Decimal Time value of 10.24 this will read 10*

6) Equation for MINUTES is ({DECIMAL TIME}-{HOURS})*60

*For Decimal Time value **10.24 the equation will be (10.24-10)*60=14.4 which will read as 14*

7) Equation for SECONDS is ((({DECIMAL TIME}-{HOURS})*60)-{MINUTES})*60

(*(10.24-10)*60)-14)*60=24*

So we are left with

DECIMAL TIME = 10.24

HOURS = 10

MINUTES = 14

SECONDS = 24

To string that together, you will need to create a text equation. This Text Equation will read:

{HOURS}:{MINUTES}:{SECONDS}

BUT WAIT!

In order to make sure you don't end up with all of those extra zeroes in your equation, you'll need to use a Regular expression

right(string, 2)

This takes only the last two alphanumerics in a given string of characters

So . . . the final equation reads:

right({HOURS}, 2):right({MINUTES}, 2):right({SECONDS}, 2)

**Be sure to include a space before '2')