The built-in PNG property handler does not support the tIME chunk for some reason. Why? I don’t know and it is only 7 bytes of data that is easy to parse!
We can fix this with a little shell extension. Sadly PSCreateMultiplexPropertyStore is documented to be read-only and I did not check if the system supplied version of IPropertyStore supports aggregation. We could hook the interface methods or do other tricks but just creating a simple wrapper seems to be enough to get a read-only version to work.