There are different projections. You are thinking of Plate carree but this is Mercator.
Plate carree is a special case of Equidistant Cylindrical. You can think of it as measuring the distance along the equator, and then turning 90 degrees and measuring the distance along the meridian. Then you plot that as if it were flat. For other equidistant cylindrical projections you can replace the equator with some other parallel called a standard parallel. (actually each such projection has 2 standard parallels, one on either side of the equator.)
If you are at the standard parallel, everything is fine. As you move away from it, the map gets distorted. Stretched out east to west as you move toward the poles, or pinched together as you move toward the equator (unless the equator is both standard parallels as in Plate Carree)
In plate carree, yes, the aspect ratio for a map of the whole globe is 2:1, but the projection is only generally used for intermediate data to be manipulated in other ways, or sometimes for thematic maps. It's ugly and distorts both angles and areas. If you use other standard parallels, the width is twice the cosine of the standard parallels times the height: 2*cos(latitude)*height.
Mercator is designed to preserve angles, (In fact it goes further and preserves compass bearings) and is meant for marine navigation. It does this by stretching out everything north-south by the same amount it is stretched east-west, and otherwise works like plate carree. This means that things get bigger as you move toward the poles, and as the poles are stretched out infinitely, they are infinitely far away. Notice that the parallels (horizontal lines) spread out as you move away from the equator. Roughly speaking it preserves shapes by distorting area.
So Mercator maps are always missing the poles. In this case I cut it off at 85 N/S although it's usually a bit lower, which is why most Mercator maps have a higher aspect ratio. You can cut off the excess if you want.
Mercator was used for global general reference maps for a long time, although it's not actually a very good choice for this. (The decision was made by publishers, not cartographers) Modern reference maps tend to use hybrid projections like Winkel Tripel which are generally oblong shapes rather than rectangles and don't need to chop anythting off. For a time zone map, a cylindrical (comes out as a rectangle) projection like either of Mercator or Equidistant Cylindrical does have some advantage in that it will make the zones come out as nice vertical stripes rather than wacky crescent shapes.