To properly setup pre-orders, first go to
Stores > Store Settings > Opening Hours
Select opening hours as 24h so your customers can place an order at any time of the day. It should look like this:
Scroll down and click Save to apply the changes
Go back to Store Settings and click on Pre-Orders
Select Enable to allow pre-orders. Now, choose the time slot for the pre-orders, how many orders per slot you'd like to accept, monetary limit per slot, and how many days in advance your customers can order from your store.
Order cut-off will define how many days you need to prepare the order. If you can accept orders for the same day, simply leave it as 0.
The max orders per slot will determine how many orders you can accept for every interval. When your max is reached, the time (for pick up) will no longer be available for new orders.
Then, select pickup times i.e. what days and times the orders can be delivered or collected.
You can add multiple intervals per day, as much as your manpower can handle and even set a monetary limit per slot.
Don't forget to press Save to apply the changes.