Suppliers can restrict how many passengers can be picked up for a certain activity. You may be able to accommodate 15 pax on your experience but only have 10 pick-up seats available.
This feature also allows you to offer pick up for your morning departure, but not for your afternoon departure.
Navigate to your experience via "Products" > "Experiences" and start by checking your "How to get there" settings under "Meeting & Pick-up" on the left hand side of the screen. You should have "Meet on location or pick-up" selected.
Set your meeting points and pick up points under under "Meeting points" and "Pick-up service" and navigate to "Pick-up config" where you select that "This pick-up service has a limited amount of available seats".
Now navigate down to your "Calendar" which can be found under "Availability" on the left hand side on the screen and click on "View availability".
Select the gear icon to view your availability rule/rules.
There you can add the number of seats you have available and the start times affected but you can have more than one rule.
I have e.g. made one rule with 10 pick-up seats available for two of your start times and another rule with no pick-up seats for the third start time. They will be displayed in different colours so you don't get them mixed up.