I do it between 15 and 25 minutes depending on where you are in Ancoats and the route you take, but I'm a fast walker. If you leave yourself 30 minutes, though, you should be alright. The walk across the new Islington canals, and then up the canal towards City is probably a touch longer but also a nice Manchester thing to do, especially if the sun is out, and gets you off the busy main roads.
Cutting room square is probably one of the prettiest parts of the city centre, and you could do hip hop chip shop for a twist on a match day classic, a pint in the Edinburgh Castle, which is a new "traditional" boozer, a pint in Seven Brothers, one of the city's better breweries, and then head up to the ground. But there is everything from Vietnamese to Portuguese tapas to really good wood fired pizzas on the square, and other things close again (see below). There's also a sports bar on the square if you want to watch the early kick off. I actually don't go to that part of town before the football very often, but I'd be shocked if there weren't blues milling about the place before a game.
The best restaurants and bars in Ancoats are all right here
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