The speed of the game is how fast their "clock" runs, not how fast they move around the village. If you have a nursing mother you can compare the various times for nursing:

1/2 speed: 400 minutes
normal: 240 minutes
2x speed: 120 minutes

(Yes, the math isn't exactly right. )

In all cases it is "2 years" village time.

When solving the puzzles, I'm usually playing on 1/2 speed. The villagers get more done for their "year" than at the other speeds and therefore they eat less food for the same amount of tasks.

However, if can be frustrating if I'm waiting for the crops to grow or a nursing mother to get back to work. (So I may switch the speed for a short period.)