According to the Twitch dev documentation on Drops, “Any rewards earned by viewers will remain within their inventory, if they have earned them or claimed them already.” Under the section about Expired Campaigns.
My personal interpretation of that would be that items you earned but didn’t push the Claim button for should be there for you… but I’m not the one doing implementation on either side.
But if you’re getting a notification that says you have a limited time to actually claim it, well. You should claim the item right after you earn it. You can claim without connecting your account, so the items will sit in your Twitch inventory. Then once you connect your accounts, you should then get the crafting recipes in-game.
Edit: Twitch Drops in your Twitch Inventory must be claimed within 24 hours of the Campaign end date. Each day is its own campaign, so you’ll want to claim the item immediately after earning it.