I get what you’re saying.
Are your customers uploading CSV files or using an API call for such imports?
Note that there’s no way really to guess what the date import format is, if you allow date import in various formats. Somewhere, someone has to tell the system: “OK, the dates we are sending here are in format X.”
But, once one can install NPM packages (specifically moment.js) and use them in server-side script, taking a wide variety of string representations of dates and converting them accurately to date objects would be relatively easy.
In the meantime, you’d need to take your uploaded string representations of dates, leave them as strings, get the User (or the CSV or whatever) to tell you what the date format is, and you could pass those things to an external API (like a webtask of your own design) that does the flexible string-to-date conversion and passes back dates in an unambiguous format accepted and understood by Bubble.
Moment makes that insanely easy. See the docs for moment’s string and string+format features:
You can also run moment in the page (client side) and I do this all the time. So for some use cases, you could suck the data into Bubble and then send the user to a page where the date conversion would happen, pass that back up into Bubble, and do other stuff there. (Like I said, this would only work for certain use cases.)
The general point is that string-to-date parsing is full of “gotchas” and there are robust libraries for doing this (so I wouldn’t set out to reinvent the wheel here). You just can’t at the present time execute those on the server side in Bubble. (And even if you could, it might not be the best or fastest way to do that.)