How should I write the date and time of ceremony in my invitation?

Traditionally, numbers for the wedding date and time have been spelled out in full. For formal invitations, you would write "the twenty-fourth of June", rather than "June 24th", "at three o’clock", or "at three in the afternoon", or "at half after seven in the evening".

The year should also be spelled out:
"two thousand and two".

If the invitation is informal, the date can be as follows:
"June 15th, 2002"