It uses the date format and timezone you have set in your preferences. So it would be the same format as what you see at Special:Log, for example.

Part of the reason we do this is to prevent conflicts with DiscussionTools, which will be necessary for the add/remove support functionality (T399500). We won't be able to allow for replies to votes and also provide the functionality we want. We figure this shouldn't be a problem as that's what the discussion page is for, after all. We will also migrate any existing replies to votes to their respective talk pages.

The other reason is the entity page itself is not meant to be discussion page at all. It never was – we used to have the vote format as [username] [timestamp] [comment] to prevent DiscussionTools from recognizing them, then at some point over the past year DT got smarter and still thought they should be reply-able!

Displaying the user's custom signature may be possible, but I'd rather avoid it as it would only further the misconception that these are DT-compatible comments.

That said, perhaps we should clarify things and add a message like "For discussion, please use the [Discussion page]"? I assume you aren't the only person who perceives the votes as being a discussion-like and thus believes it should appear that way.