It's hard to tell if it is too early since you didn't give us any information about where in the world you are. But most parts of the US, it would not be too early. My daylilies are almost finished blooming. And if your other daylily is blooming that is a good argument that it is not too early.
Yes if the slugs did enough damage to the leaves to cut down the energy the plant was getting, that could keep it from blooming, though daylilies are usually pretty tough and hardy and can survive a fair amount. But especially this being a young plant, just planted last year, it could have been set back like that.
Deal with the problem, but you may just have to wait another year for the blooms.