Children cut out four jobs and use them to show counting on methods for time . For example, start at 8 am first job they choose might last 15 mins to so they create a number line , put the circle cut out at the top of a jump and then calculate the finish time as 8:15. Easy to differentiate, less able can just choose jobs that last an hour, more able can be given more specfic requiremnts e.g. they must do four jobs within three hours etc. Prior to this, I would ensure children can use a number line for counting on and durations of time.