It's sort of like calculating the probability of a hash collision. The speed at which the monkeys type is also a factor.

How fast do monkeys type?

Just give them a typewriter that records the position of where the key is pressed to a million bits accuracy, convert that to a series of ASCII characters (through a hash function), and the monkeys will type very fast.

That’s really funny. Give the keyboard a big enough buffer to hold Shakespeare and flush it to the screen on startup. With infinite monkeys and therefore infinite buffers the monkeys don’t even have to type!

>> For the timescale calculations, we assume that a monkey typist presses one key per second every second of the day