One-hour calendar block, say (4)

I believe the answer is:

slot

(Other definitions for slot that I've seen before include "This gaming machine operates by insertion of coin" , "Fit into puzzle" , "Scheduled time -- aperture for coins" , "Long narrow opening" , "Space for inserting coin" .)

I've seen this clue in the Universal.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.