Gavin
Since your warranty period has started, it is only fair that you should put it all together and make sure it works. Three weeks of testing sounds about enough. You might also run into the "I need just one other bit" problem, and you wouldn't want Xmas spoilt by not having it and the shops being closed.
SWMBO permitted me to buy a scope for my birthday last year. By the time it arrived, birthday was passed,so I didn't have to justify opening the boxes. It's all the other boxes since then that had to be justified.
Andrew