Agreed that the derailleur shouldn't take more than a minute, tops. Next time take a good photo before detaching it so you know how it goes back on. Even if the frame fits into the box OK with the derailleur attached, it really should come off in case the bike shifts in the case (because no matter how tight you strap it down, something WILL shift). Leaving it on is asking for a bent derailleur hanger and an extra trip to the bike shop.