There are a lot of things the kit has to do, including resolving earth horizon and true north (matching sensed earth rate with position to establish notional axis 'alignment') and so on. Real black box stuff! It takes that long to fine tune all the results to give the required accuracy. It could have a working 'alignment' in a couple of minutes but the platform would not be accurately 'aligned' and the drift would be significant over time. A 'rapid realign' starts from a platform that is 'aligned' and merely zeroes all the accrued position/ground speed errors but any platform 'misalignment' is not removed so the errors will build up more quickly after.
The further north/south you go (nearer the poles) the lower is the earth rate in the roll and pitch sense and it becomes more and more 'yaw' only, reducing the number of factors it can use to 'align' the platform to achieve a heading.
A bit 'simplified' but lots of alignment info via Google if you look.