Most Customers will pickup after you tell them the Invoice is ready.

But when they request,  and you give them a date,  you should enter it in the system.   The calendar can then remind who to expect.  

You can add/remove a Pickup Date like this:

1. Navigate Tags -> Open.    
2. Find the Tag by searching Tag column or entire list
3. Click on the Tag # underlined link.  It takes you to the Tag Detail page in a New Tab.
4. Select a date from the calendar or blank the date to remove.
5. Click Save button
6. Close the Tab by clicking the small x  or the button X

The Pickup Date column is normally not displayed on the Tag list.  This is because MOST Tags will pickup when they have been notified.

But you can switch the View to "Pickup"  and see those who have been given a date in advance.