I see your items now say 1-3 days to ship. So if you cannot make them that quickly, no matter what the circumstances, then you need to follow Bev's advice and have them ready to ship, or you WILL get bad reviews.
I don't believe most customers even look at the shipping estimate, judging from the questions I get about that. So anyone who has longer ship times would be wise to send a thank you for the order, and "btw did you notice that I need _ days to produce that item?" message to their customers.
Maybe the new shop will place the ship times more prominently, along with policies.