It depends on your partitions. During an upgrade, it will shrink your main partition to increase the recovery partition. The sizes have changed in this Windows update. They did in one of the previous updates too. If the disk still has unallocated space, then this is quick, no resizing needed for the main partition. But if not, this is going to take time, data needs to be relocated. In the end, if you've been upgrading W10 from the beginning instead of installing new, the partitioning scheme on the disk is a complete mess.