PHP calculate half of 8 hour working day

We have `Moodle` `plugin`, where we add the `travel time` of each employee. Until now, we calculated the duration of the travel time in `days`, as we added the data for every employee only in such form `timepickup`- 21.10.2105 `timereturn`-23.10.2015. The data was being added in the function here: $user->timepickup = gmdate("Y-m-d H:i", $timepickup); $user->timereturn = gmdate("Y-m-d H:i", $timereturn); And the calculating of the travel time here: $datetime1 = strtotime($employee->timepickup); $datetime2 = strtotime($employee->timereturn); $interval = $datetime2 - $datetime1; As you can see, we add the option to import the `exact time` in `hours` and `minutes` of the `timepickup` and `timereturn`. How to calculate the travel time and display it in `days` and `half days` (we assume, that `half day` are `4 hours` from the `8 hour` working day. So instead of travel time `1 day(s)` for adding `timepickup`- `21.10.2105 08:00` `timereturn`-`23.10.2015 12:00`, we will have displayed `0,5 day(s)`.