Plymouth Rocket can help manage curbside pick up with Ekregistration.  We have libraries using our forms in two different ways, with time slots and individual forms for blocks.  

Sample Form with Time Slots:
http://www.eventkeeper.com/code/ekform.cfm?curOrg=KN&curName=2020/05/29_Book_Pick_Up

How to set up Time Slots: 
Time slots are made in the Advanced forms in the custom fields section.  If you do not have EKReg advanced, then you can try using the block form below.

Instructions:  www.answerkeeper.com/ekreg_timeslots 

How to set up time blocks:
Time blocks means that you have set up an event for a set time block and assigned a form to that block.  

Example:

June 1 9am-12pm - Book pick up block 1
June 1 12pm - 3pm - Book pick up block 2

Then make a form with a max number of registrants for each block.  You will then have several registration forms for the same day, but each form will cater to a different time.

Check out our sample library to see the set ups in action: http://www.eventkeeper.com/code/events.cfm?curOrg=KN