Most point upgrades are about squashing bugs and rolling out minor feature enhancements. But today's iOS 10.3 update is more than that. As we mentioned earlier today, this update changes the underlying file system from HFS+ to APFS.
While we'd hope the update process has been tested thoroughly there's always a chance something can go pear-shaped and brick your device. And while recovery from a failed update is not impossible it's a major league PITA.
My suggestion is to wait 24 hours in case a bug is detected by the early adopters (it's been known to happen and for Apple to pull updates), make a backup of your iPhone or iPad, and do the update at a time when some unscheduled downtime isn't going to interrupt your work too severely.
If you're an early updater, let us know your experiences in the comments.