The phrase "a late hour" is correct and usable in written English.
It can be used to refer to a time that is considered late in the day or night, often implying that it is past the usual time for activities or events.
Example: "We decided to leave the party at a late hour, as we were all feeling tired."
Alternatives: "an advanced hour" or "a late time".
At a late hour, my mother picked up the phone and made a call.
Much is avant-garde and probably better appreciated at such a late hour, after a few drinks.
The railway strike was in operation all over the country yesterday [Aug. 18], but at a late hour last night negotiations for peace were still going on.
Three times they have been expected home by their families, and three times the tour has been extended at a late hour.
The players were ticked off, posing with visiting fans at a late hour in an era when social media makes something local international instantly.
In its 23rd year, the three-day Rendezvous barely survived this city's bankruptcy, with funds for police protection and other services having been scraped together at a late hour.
I have gone to Oscar parties in the past, but I hate that get-up-and-go-home-at-a-late-hour feeling.
Matthias Holle sang Gurnemanz with touching dignity, although his appearance in the part came as a late-hour surprise.
Laura Aikin, a late-hour substitute for the soprano Susan Gritton, sounded uneasy at first, more settled after intermission, but a little fragile throughout.
But in a late-hour compromise, the bill does not include the tough restrictions on derivatives trading championed by Senator Blanche L. Lincoln, Democrat of Arkansas, which would have forced banks to jettison their most lucrative dealings in this area.
A lot of the afternoon was to have been about the French soprano Natalie Dessay, who pleaded a late-hour case of bronchitis and gave way to the mezzo-soprano Michelle DeYoung.
