There is no management pressure. The article mentions that the artist took it upon himself to start making the signs. So I'm under the impression he does so within his free time.
I suppose if the job is helping direct people, he will have his hands full during rush hour and have all day in between to contemplate the signage needed most.
The mystery to me is how he's allowed to block off large sections of floor/wall for hours to make them. You'd think management would be cross about that, at least.
Due to the medium, he must be doing the laborious work onsite.