Percentage of time spent on various stages of a game

In a non-electronic game, the time spent by the designer and developer (this is sometimes two different people) is approximately:

10-15% Design
10-15% Prototype production and initial testing to arrive at a full set of rules that works. Most of this time is spent on the rules, not the physical prototype
75% Development: playtesting and revision

For an electronic game the percentages are different. I confess for electronic games I am "pulling these out of the air", they are estimates, and undoubtedly will vary greatly from one company to another.

10-15% Design
60% Production of a developmental prototype (this is very time-consuming)
15-20% Playtesting and revision of that prototype
10% Testing for programming bugs

This is "actual", not desirable. Blizzard works with no deadlines because they can easily self-fund projects. They can say "the game will be released when it is done". Most likely they spend more time on a game than the typical development studio, and a lot of that additional time is spent on playtesting and revision of the prototype. So their percentages would be different. This is the way the game ought to be made, but few companies have the track record of success and constant influx of royalties that Blizzard enjoys, so they can't afford to do it that way. This helps explain why so many newly-released games are seriously buggy.

We have to be careful about the word "prototype". Electronic game prototypes are often very limited versions of a game produced to get some idea of what it will actually be like, and are part of the design process; they are then discarded and work begins on the actual game, which ultimately arrives at a "developmental prototype" that can be turned into the game that will be sold.