Different parts of PATH closes at different times. Some parts of PATH have stores/restaurants staying open to 9pm or beyond.
AFAIK, the Union restaurants will be open late.
Worked on Bay St. Most food courts underground. I worked on Bay street and 90% of the food courts I ate in were all subterranean, some good, some soso, and Eaton Centre's Urban Eatery is a very good subterranean food court. Union's complex of gastronomy will be in that league of "fanciness" (approximately), and in some ways fancier (there's no sit-down as fancy as now-opened Amano in Urban Eatery).
Union already attracting lunch worker traffic: I now hear reports that people are coming into Union to eat lunch, from the surrounding skyscrapers. Massive food court market, that is quite insatiable. As long as more York-side PATH connections open (eventually), I think the Union food court will succeed.
Lame York-side PATH: The problem arises in the lame York-side path connections and the pre-RER era, which means there might be a bit of a struggle between 2018-2025 for some of the shops, but the rents will still help pay for Union's upkeep, merely from the lunch market alone. After 2025, I have no doubt on the vibrant popularity of the subterranean food court.
Overcrowded food courts at lunch: Unless you've worked on Bay Street like I have, you can't believe how hugely popular the subterranean food courts are. Overcrowded. We need more food courts downtown, IMHO -- purely based off my own personal experience as an IT cubicle office worker. In many food courts, it is literally more than 10x more massive profits than the condo market.
My Experience As a Lunch Lemming: Workers often PATH-over 1 or 2 buildings, so it'll capture a lot of downtown office-worker market as a Relief Food Court, lightening the loads on their respective food courts, which then cascades into business for even-further-adjacent buildings, in a cascading effect that flows all the way to far beyond Eaton Centre. Any new food court that opens downtown is promptly instantly filled with office workers at lunch in a major induced-demand flow/contraflow. In a new equilibrium, all overflowing again. I've seen it happen over the years. Sure, some workers eat at their desks because food courts are full and lineups are too long, but that's a massive latent market of office workers who will go to a nice food court with good, healthy food.
Lamenting York-side PATH: That's why I lament the delayed/postponed York-side PATH connections, and lack of Royal York connections to elsewhere. I almost think we need to force Royal York to force them to open their bottom level as a pedestrian expressway in multiple directions, east, west, and northwards.
Even lunch success may not be enough: And secondly, while lunch success is all but assured, even the lunchtime may not be enough to pay for expensive Union rents, even if I already know that Union food court will be busy at lunch (I can assure you it will be) -- you probably need breakfast, lunch and dinner business often to just pay for the rent. So that's why turning GO into a metro equivalent (RER/SmartTrack/whatnot/etc) will likely be needed to make sure that the food is busy.
Anticipated moat openings will help: Nontheless, TD Carriageway will pull in the lunch market into the York concourse with a fairly short walk from many towers to the west/northwest, since there's very good sidewalk entrances now. It'll be an easy walk once the TD Carriageway is finished, but it may require an outdoor hop (ugh, winter) until more PATH links are made on the west-side.
Even today, evidence is now showing lunchtime surges at Union, now that business workers are discovering Amano. Reportedly, it filled up nicely at lunch with mostly non-commuters. Promising start.
