The update weighs a little over 600 MB so maybe you’ll want to ensure you’re over a WiFi connection before proceeding, and also to ensure that your device is charging while updating, lest it dies halfway during the update process. As noted by AppleInsider, the update to iOS 10.3 seems to take a little longer than expected as this is apparently due to Apple making the switch to APFS.
They discovered that these installs are taking more than 20 minutes on devices like the iPhone 7 and 7 Plus, and nearly 50 minutes with the iPad Air 2, so like we said, you’ll want to make sure your device has enough juice before proceeding. The iOS 10.3 update will bring about a bunch of new features such as the Find My AirPods feature that helps locate missing AirPods, and more, such as various bug fixes and what not, so maybe this is an update worth checking out.