How long should I spend at Niagara Falls?
Honestly? You can see the main falls and get the classic experience in about 4-5 hours if you're just doing the basics: walk to the brink, ride the Maid of the Mist (about 20 minutes on the water, but budget 90 minutes with lines), and hit the Cave of the Winds (another 60-90 minutes). If you're in a rush, even 2-3 hours works for a quick look and a few photos. But that's like eating a steak in 5 minutes—you'll miss the whole point.
If you want to actually enjoy it without feeling like a cattle call, plan for a full day. That lets you do the boat ride, walk across the Rainbow Bridge for the view, grab a decent meal (avoid the overpriced tourist traps on Clifton Hill), and maybe hit the Niagara Parks Botanical Gardens for free. If you're staying overnight, you can catch the fireworks or the illumination at night, which is honestly way better than the daytime crowds. For the Canadian side, you can also tack on a trip to the Skylon Tower for a view—but skip the overpriced restaurant.
Bottom line: Half-day for a drive-by, full day for the real deal. Anything more is overkill unless you're doing the wine trail or going to Niagara-on-the-Lake. And no, you don't need 3 days unless you're bringing kids who want the Ferris wheel and haunted houses—that's Clifton Hill bullshit, not the falls.