The British spelling here of “honour" (with the “u” added) should be strictly reserved for weddings in a house of worship. Use the “pleasure of your company” at other venues by omitting honour or honor.
Spell out the year omitting the “and”, for example, “Saturday, the twenty-second of September, two thousand eighteen.
“half after” instead of “half past” or “six-thirty”.
EmilyPost.com includes all things mannerly including protocol and procedures for all weddings: formal, traditional, and otherwise. It’s worth a gander. Great tips on other “must-do” lists, such as acceptable thank-you notes in this digital era. Hand-written notes are still the preferred method to extend your sincere thanks.