Apple Trade in

So I have an iPhone 7 Plus and I’m planning to buy the new 14 pro. However I am unable to trade in the iPhone 7 right now for personal reasons before I buy the 14 pro. My doubt is that if I wanna trade in my iPhone 7 Plus…can I save the credits and accumulate it to buy another apple device in the future ? Or must I buy an apple product the very same time I trade in the old 7 plus