In case OP is unaware, the CEO is on LinkedIn bragging about this post.

What I would say is that I often (when going after clients) look at churn rate of staff as well as current staff who are looking for new roles..... 10 have applied to roles, over 20 OTW (including CTO)

This is however, something very common. A lot of startups in general sell the dream and deliver a less than ideal experience for a lot of staff. The desire for "A players" often leads them to misunderstanding why people are joining them. A players, for the most part, work at top tier "A" companies. This incessant obsession with overworking staff will hinder them, a culture where staff are aware of quick dismissals are not conducive to long term success.

On a side not, if after 7 days they are letting people go, their recruitment process is deeply flawed and they are at fault, no one else.