Amazon does allow you to set a restock date on your listings, but SKULabs stock sync will overwrite that date the next time it runs for those listings. There are two possible workarounds for this:
Set the restock date and quantity for these listings in SKULabs so that SKULabs syncs the restock date and quantity to Amazon.
SKULabs syncs restock date and quantity when all of the following conditions are met: The item is out of stock, the restock quantity is greater than 0, and the restock date is in the future.
Open the relevant listings in SKULabs and set their stock sync rules to "skip". This will exclude those listings from SKULabs stock sync until you change the rule back. Now you can set your restock date for those listings on Amazon.
Don't forget to return to SKULabs when each restock date is met so you can re-enable inventory sync once you've received the relevant item's stock.