What is the timeline of a rainbow table generator?

 I've been reading up about rainbow tables as I think they're quite interesting cause they're actually a pretty simple concept.

Anyway, I was wondering, has anyone been involved in actually generating one? How is it possibly done? I just don't see how it is actually possible to generate every combination of every character.

If we exclude special characters, there are these numbers.

ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz 1234567890 That sounds like there is 26+26+10 = 62 characters

Thatmeans that a password of length 8 has 62^8 combinations.

which is equal to 218340105584896

That alone sounds like it would take ages to generate. What about when we increase the number of characters to 12 and add in the special characters (say there are another 10 of them just by looking at the characters that you get by pressing shift - number)? We would get 72^12 = 19408409961765342806016 That's a number that's big enough to take years to get.