You don’t need php at all to achieve what you are after.
This can be done with just css.
This shows the title and excerpt by default.
.wrap .wp-tiles-byline-fade-in .wp-tiles-tile-with-image .wp-tiles-byline {
opacity: 1;
}
This hides the excerpt again now that we have revealed it.
.wrap .wp-tiles-byline-fade-in .wp-tiles-tile-with-image .wp-tiles-byline .wp-tiles-byline-content {
opacity: 0;
}
And this shows the excerpt again when you hover over it.
.wrap .wp-tiles-byline-fade-in .wp-tiles-tile-with-image:hover .wp-tiles-byline .wp-tiles-byline-content {
opacity: 1;
}