This site offers many free math games that allow you to practice time calculations and conversions in days, hours, minutes and seconds.
The little math quiz (time)
The little math quiz collects a set of small fun math exercises to do online for 7-11 year olds.Duration calculation game (time)
This game on time calculations allows to practice manipulating durations expressed in days, hours, minutes, seconds (d, h, min, s).Time conversion game (time)
This game allows you to practice making conversions on days, hours, minutes, seconds (d, h, min, s).