Hour and half max... I mean... MAX!
Here's the thing though, you have to be set-up for speed to knock them out. AND the banner guy has to know his job, and understand order of operations to make moves the most efficiently as possible.
OK, picture this: If the banners are printed, all he has to do is unroll the banner as long as your table is. Say it's a 12 to 20 foot table (common size in most shops) Then he needs to run a length of banner tape all the way down both sides. Then go ahead and hem the long banner both side. Only need to cut the banners out of the long roll and add end hem tape, if that's what they call for. Hem, hem... bam! Then when all the banners are hemmed, bust out the grommet press. Do all of the same corners at once. (You gotta keep the upside down movement of a banner to a minimum to keep from scratching them)
I'm honestly gonna say I can probably do it under an hour. But I'd be hauling ***, with a point to prove. Especially if I had a lazy or slower paced employee... I'd show them how it can be done, and how I expect them to work when work is on the table. Because we have a lot of goof off down time between jobs, but when a ticket gets pulled, it's "GO TIME!"
Now here's where I see I can have it done even faster (IF YOU WERE SET-UP PROPERLY FOR BANNER OUTPUT)
If you are set on banner tape as your method, get a Banner Cyclone. If you like seam welded banners, get a WeldMaster. If you like sewn edges, get an industrial, double needle with walking foot. That may take an experienced person to run however. I don't expect many people to have industrial sewing machine operation experience. But you can learn a WeldMaster really fast. Plus with a WeldMaster, you can get double sided in-line grommet punch. Pie-In-The-Sky-Pricey, I know... but if that was your market, you'd kill it all day long.
But let's say you got a Banner Cyclone. They are only $2500. Now you need a banner station for grommeting. I've made these 20' long galvanized sheet metal angled wall tables. Galvanized, so you can use magnets to hold the banner in place. Then I got a length of aluminum extrusion, and a lineal guide rail that matched. And mounted a pneumatic grommet punch that slides back and forth. You can pick one up at the sign show for a song and a dance. While it's not a fully automatic grommet punch machine, it's at least button operated and way quicker than the lame-o handle style.
Again, if this was your niche, you'd be foolish not to optimize this operation to be as quick and simple as possible. Time is money! Bam, bam bam! Get them out the door. They aren't works of art, they're banners.