Technically no. But practically, possibly, yes.
Time is an absolute measurement using an agreed standard (UTC, hours, minutes, seconds, etc...). It's a human construct to log a progression of local (cosmically speaking) events against. By its definition, it requires a "witness" to validate, which is the same as saying "authority".
Note: It's very important to consider the application of what you're trying to achieve with a time-like stamp without an "authority". You might have a very specific problem in mind, which might have a specific interesting solution.
Does this mean that there's nothing here to discover/invent? I don't think so. The problem is "time". I suspect, if you remove "time", and step back toward a more universal fundamental of "events", you might have a better chance of achieving your background requirements.
Consider, in a hostage situation, they will ask a hostage to record their plea while holding a current newspaper. Why? So they know the video was recorded very recently. Absolute time is a factor of the proof here, but importantly so are "events". The time is implied by the newspaper edition, the content, and the fact that no one can predict the future (tomorrow's newspaper). This doesn't work in digital timestamping type scenarios of course, but it helps to describe how "events" may be key, not quantum-level events, but most likely more macroscopic events.
Picture of the night sky
Here's a poor, but workable option which shows there may be hope. The planets, constellations, and more have been used for hundreds of years to determine "time". Manuals are required to map such cosmic "events" to our agreed standard of "time".
One could take one or more photos of key features in the night sky, possibly also requiring telescope(s), with superimposed hash value in the image.
There are many other possible schemes for making the night sky, but most (if not all) require a photo. Of course, it's possible to photoshop, so it's not perfect. Also the time precision is relatively low.
Going back to "applications" and context. If your purpose was to ensure that you paid money before a package was sent, then it's all relative. It doesn't matter what the time is, you only want to determine which event happened first. This doesn't necessarily require an absolute event reference (space). If you're both in the same room hand over money, and then hand over the package, you see it happen. If you do this from a distance, you need a witness/authority/third-party.
So technically the way we do it currently is for a reason, no other compelling way has been found yet. The same issues compound problems with HTTPS certificates involving revocations list, OCSP stapling, and more.
It's good to step back to analyse the problem in more conceptual abstract ideas to answer such questions.