Night work tonight at B4 site, as foundation concrete work starts at 10 pm, continues through "Saturday evening"

A message yesterday from Empire State Development regarding night work tonight at the B4 (18 Sixth Avenue) site at the northeast corner of the arena block:

Pending final permit approval from the Department of Buildings, foundation concrete work will commence on Friday evening August 9 at approximately 10:00 PM and continue through Saturday evening August 10. Appropriate noise, light, and dust mitigation practices will be implemented.

It does not say why foundation work must occur after hours--convenience, most likely--or how long through Saturday evening it would continue.