telescope - When is Gamma Draconis closest to the zenith in London on April 4th

I am reading Roobert Hooke's paper An attempt to prove the motion of the earth from observations (1674, faksimile). Hooke writes

The principal dayes of doing which will be about the 4 of April, when our Zenith passeth by the said Star at midnight

The said star is Gamma Draconis, and the observations are made in London. As far as I see it, the star is closest to the Zenit at 6 in the morning in London at April 4th.

So, why does Hooke say at midnight? Is this an expression of the 17th century?