Both formulas produce results like 4:6 or 6:0 when I hope to see 4:06 or 6:00.
How did you avoid those?
ROUNDDOWN({Time Available}/3600, 0)
& ":" & ROUND(({Time Available}/60) - (60*ROUNDDOWN({Time Available}/3600, 0)),0)
ROUNDDOWN(({Time Available}/3600), 0) & ":" & ROUND(MOD(({Time Available}/60), 60))
Update, used instead:
DATETIME_FORMAT(DATEADD(TODAY(),{Time Available}&"",'s'),'H:mm')