The way that this is handled on most websites is that you show "X time ago" but you can hover over the time to get the full timestamp. For example, that's how it's handled here on Hacker News and Reddit.
Honestly, the fact that mobile browsers don't provide a way to see the contents of the title attribute is a severe UX failing on the part of the browser developers, not the website developers, who are literally using the attribute as intended.