There is a feature that will allow you to check all grooming appointments in and out at the same time.

Please note:  This feature is only available for today's date.  It is not available for past or future dates.

Click on File, System Options, Grooming tab.

Make sure the box for "Disable Check All In/Out feature" is not checked.

On the grooming schedule, there will be buttons for Chk All In and Chk All Out

Click the button and choose which pets you want to check in or out.  You can choose all pets (Select All) or specific ones by clicking the X boxes.