It's actually hard to say for sure where the framing is around the window opening, different for common residential framing and commercial construction, etc.
You say the window opening is 30" so let's say the jack studs are 36" apart. According to the page you linked, the mount is about 39" wide, and it looks like the outermost mounting holes are about 37" apart, so it would just barely work. If there are any miscalculations, you could have a headache.
Consider this, if there's molding around the window, you'll want to put something behind the mount so it clears the window, maybe a piece of 3/4" plywood that's the same height as the mount.
If you make that piece of plywood a little wider - say 6" wide - you can attach that first, hit the studs with the plywood with several screws, then attach the mount to the plywood. This gives you some flexibility.