Creating a 45 minute movie in one chunk (which is what I imagine you mean from your post) and expecting to export it all in one go without any problems is being slightly optimistic, to be honest
![Smily [:)]](/emoticons/emotion-1.gif)
That said, no, unfortunately you can't delete more than one scene at a time in PP (or AMM). You can speed it up a bit by clicking to select the scene you want to delete and pressing the "DEL" key (rather than dragging it to the bin icon and dropping it), but other than that, you can't block select scenes.
Also, be aware that, once you've completed the filming, if you take the movie back into AMM to refilm scenes then put it back into Post Production, the timings and cuts of your scenes will all change back to their original filming order (incredibly annoying if you've spent ages correcting things, cutting scene snippets and repositioning them, etc).
That's one of the beauty's of outside editing; you can film one sequence, export it and do everything else (except lip synching) out of the game, removing the annoying sound synch bug that can affect long movies exported direct with sound added in-game.
Machinima maker? Using The Movies? iClone? Moviestorm? Any other engine? Then check out TMUnderground at (http://www.tmunderground.com/)