It very important to be able to rebuild and fix your heli, we all crash and need to be able to fix them easy and quickly, building your heli with all the bits in good shape will help you find the bent and broken bit's after a crash,
learning to set up your heli is very important and we can set them up to fly the way we like, it's one of the things I like about modern heli's. knowing how to rebuild your heli and how to set it up will save you lots of time in the long run.
The build time for a align 550 is a bit like how long is a bit of string, I can build one in one to two days but if your new to them it might take 3 to 5 days to build and set up well enough to fly, I like to do it the best I can, I grease all the bearings and only use lock tight on a few bit's, I'm not a fan of lock tight, it makes it more likely to strip the threads or round of the heads of the nut and bolts after a few rebuilds,
I can't recommend highly enough that you build you heli, knowing how it goes together when it's new and strait will save you lots of time later,