The Check'In has different detection modes, described in this article. To schedule a mode change, simply go to the page of your sensor. Click on "Settings", then on "Calendar", and finally on "+ Add schedule".
Choose whether the schedule is recurring or a one shot.
Once this is done, select the detection mode of your choice. You can also choose to activate or deactivate the siren during the duration of this schedule. Finally, click on "Save".
You have the option to edit or delete your schedule by clicking on it.