Error Message about starting and ending dates

Hi,
I’m using the Timed Content plugin with the Weaver Xtreme theme. Right from the start (directly after installing the plugin), every new rule I create comes with an error message:

“Warning!

Some problems have been detected. Although you can still publish this rule, it may not work the way you expect.

Starting Date/Time must be valid.
Ending Date/Time must be valid.

Check that all of the conditions for this rule are correct, and use Show Projected Dates/Times to ensure your rule is working properly.”

There’s also a button to check the invalid dates, when I click it, start and end dates are the same, but I cannot change them. They don’t match the dates I actually set and I can’t find a way to fix this problem.

I tried deactivating every other plugin, as well as using the twenty-fifteen theme without any other plugins, but that didn’t help. I really do need this plugin, so any help would be highly appreciated.