Just because somebody's a "team leader" doesn't mean much.
.visible is nothing more than a simple boolean variable, the difference in cost is either zero or basically nothing.
.visible is a property, all bets are off.
Assigning to a property is one method call, and retrieving the value is another.
In that case, the separate assignments might be faster, but watch out for another problem.
Properties have some nice properties (!), but I've seen them treated as if they were free, performance-wise, when in fact they can be major sink-holes of CPU time if they are implemented recursively.
In terms of style, I take a dim view of giving this more than a nanosecond of thought.
Nearly all serious software has far bigger issues than this.