Visitors planning a Tuesday trip up Toronto’s CN Tower should check the clock before they go. The tower’s operator has announced that a portion of the Main Observation Level will be unavailable from 3 p.m. until closing on Tuesday, October 20, and that the landmark will close fully at 10 p.m., with last entry at 8:30 p.m.

The restriction is narrow rather than a shutdown. The Lower Observation Level, the 360 Restaurant and The Top are not affected by the partial closure, according to the operator’s notice, so most of a visit — the glass floors, the restaurant and the highest viewing areas — remains available.

The notice did not give a reason for the one-day restriction. The tower remains a featured venue for the Toronto Biennial of Art, whose light installation continues through December 20, and the partial closure falls in the middle of that run.

For anyone with tickets for Tuesday afternoon or evening, the practical advice is simple: arrive earlier in the day for the full Main Observation Level, or plan the visit around the unaffected areas. Regular hours resume after Tuesday’s early close.