Very cool. How robust is the english parsing? For example, would it understand something like "The first wednesday of every month"? Either way I will definitely check it out.
You can see the grammar and lots of examples at http://bunkat.github.io/later/parsers.html#text. For your question, it would be 'on Wednesday on the first day instance every 1 month' or 'on the first day instance on Wed' would also work.