I am wondering if there is a reliable way to time-lock some of my Ethereum similar to the way coinb.in works for Bitcoin?
IMO if it's can be programmed in the smartcontract. I guess what you need to create the new smartcontract through new wallet to be used to implement that function dude.
I think that can be easily learned by you consider there are some tutorials on the youtube. Try to browsing for the function and how to implement it dude. I think this link will help you a lot dude and what you can do to visit my link
https://medium.com/cryptexfinance/how-to-create-time-locked-functions-523424def80