userstyles.org - Charlie Park

This style simply drops the tweet's metadata (the part that says "less than 5 seconds ago from web") to a new line. It also right-justifies the metadata. It also adjusts the line-height, so the metadata has a uniform line-height with the general tweet copy.

When you're not hovering over a tweet, the metadata ("about 1 hour ago from web") is invisible. When you're hovering over the tweet, the metadata shows up. Easy.

Recently, Twitter added some padding to the "what are you doing" box. All this style does is remove that padding, and make the textarea box a little taller.