DHT (with data duplication, obviously), I said already. Or gossip protocol. You don't need consensus, and blockchain doesn't give you one either.
> Your answer isn't enough to solve my problem.
As you have stated the problem? Yes, it is enough.
Maybe there are some requirements that make a timestamping protocol necessary, but you haven't provided any. As I said previously, if you use blockchain, you have to defend your choice, because most of the people who build on top of it don't understand it, use it in stupid ways, and just want something trendy for the sake of being trendy. You need to prove that you aren't one of them and that you are competent with it.
> Although blockchain is not the only correct answer, blockchain is one of the solutions.
Very expensive solution, applied because you don't understand what it is and why and when would you need one (if you did, you'd explain the necessity for blockchain long time ago).