This would be especially handy because BYOND doesn't seem to honor the specified framerate. world.tick_lag is stored to two decimal places, so setting world.fps to 59 or 60 has the same effect:
10 / 59 = 0.16949...
10 / 60 = 0.16666...
Both get truncated to 0.16, and 10 / 0.16 = 62.5, which gets rounded to 63. So if you do this:
world.fps = 59
That'll output 63 twice. This isn't a huge problem, but if you set icon delays to 0.16666 expecting a rate of 60 frames per second, it might not work out like you'd expect if the game is actually running at 63 fps (or 62.5 fps).