errr, its really by day with start & finish times(even if the finish time rolls over to the following day) then everything else is worked out from them, it’s got a tad complicated (so it can be user friendly), but it’s a bug that can be rectified fairly easily since it’s still a work in progress.
an Easy rule of thumb if your shift goes over 13 hrs then your oa reduced daily rest unless you’ve had 3 solid hrs off during the shift then it beomes a split daily rest easy really