It's funny just thinking about it. Because if you are not depending on a third-party, then you are depending on yourself only. Which means that once you encrypt something hoping that you won't be able to decrypt for some amount of time, you accept that changing of the time has something to do with the decryption of your encrypted message. Since you can certainly know how much of time should be pass, you can't keep secrets from yourself right?

So, in a sense, in my opinion, if you want to encrypt a message and send it to someone and make it timelocked without a third-party, you might as well just keep the message secret until the desired amount of time has passed and just give it to him.