Katie, I don't know of an auto reply on Etsy without the vacation mode set. You could put the info in your shop announcement and on your policies page.
Other than that, if a sale is made, you have the ability for an automatic message to the buyer telling them when the item will ship. You can set that in Info and Appearance>Message to Buyers.
If you are replying between the hours of 8AM to 4PM daily, that seems reasonable. It's not like you are letting days go by before you reply.
But if there is an auto-reply to convos, I'd like to know too!