Sometime in April, Microsoft's update servers will begin delivering the Windows 10 Creators Update to current installations of Windows 10 that have been running for at least 30 days.
With hundreds of millions of PCs to update, this rollout could take a while.
And that update is a big one: roughly 3GB in size. Although setup should be quick (less than 60 minutes) on reasonably fast hardware, you might want to wait. Maybe you're traveling and don't want to deal with a major upgrade just now. Or maybe you just want to watch what happens to other people before you commit.