Use the Set Variable to Text %CurrentClipboard% action to copy the value into a variable.
Use the Set Variable Time to Calculation Value MOD 60 to get a time Seconds component. Format as 00 to ensure it uses two digits.
Use the Set Variable Time to Calculation ((Value - Seconds) / 60) MOD 60 to get a time Minutes component. Format as 00 to ensure it uses two digits.
Use the Set Variable Time to Calculation (Value - Minutes * 60 - Seconds)/3600 to get a time Hours component.
Then Set Clipboard to Text %Variable%Hours%:%Variable%Minutes%:%Variable% Seconds%
Something like that should do the trick.