Sunset and the 3rd nite begins on the 17th on a Saturday.
A complete Biblical 24 hour day begins at sunset. The 14th is Wed., at sunset the 15th nite begins at 6PM and is Thursday, etc., the 16th is Friday, and the 17th is Saturday. They came about 12 hours after the Saturday Sabbath had begun. About 5 AM just before sunrise of the same date, the 17th.
Blessings in your search for TRUTH.