I don't know how long it is "supposed" to take, but you can compile a Linux kernel (27.8M lines of code, though a good chunk of it probably isn't going to be compiled anyway because you don't need it, and another good chunk is architecture specific) in under 10 minutes on relatively modest (but modern) hardware.

On the other hand, something like Chromium (25M lines of code) will take about 8 hours, and bring your machine to its knees as it consumes ALL available resources (granted, last I did this I only had 8GB of RAM, and I was running my desktop at the time... including Chromium). I don't remember exactly how long Firefox takes to build, but I remember it was significantly less time (maybe 3 hours?).

So... it depends? On a lot of things?

(btw, LoC numbers were pulled from the first legitimate looking result I could find on a quick search... take with a grain of salt... also, compilation times are a rough approximation based on my observations... that it with a truckload of salt)