Trains – Contradictory Information: Does the Hikari 535 Shinkansen exist?

Short answer. Hyperdia is correct; You can take the Hikari 535 service at 20:33.

Long answer. Hikari 535 is an irregularly scheduled service: There is no regular schedule such as "every day" or "every day of the week", but it will only run on certain days, presumably when high demand is expected. The timeline you link to, published on JR Central's English website, does not show any such services. Hyperdia shows it. You can also view the full schedule published on JR Central's Japanese website. Hikari 535 runs on the 14th, 20th, 27th and 3rd, 11th, 17th and 24th of February. (Schedule not yet announced from March).)