Why the Brewster Buccaneer could not simply arrive earlier

Should the Brewster Buccaneer have entered service much earlier than 1941?

It would have been useful earlier, but it was not ready before its testing and training process was complete.

Service entry is the end of a development chain rather than an arbitrary date selected by the operator. The Brewster Buccaneer could not appear before 1941 unless its specification, design, and industrial work also moved earlier. Trials had to show that the aircraft and its systems functioned before squadrons could receive it. Production preparation and crew training then imposed their own schedule even if the Navy urgently wanted the capability.