Can I enable iCloud Photos synchronisation simultaneously on iPhone and iPad?

I have an iPhone running iOS 18.3.1 and an iPad Pro running iPadOS 18.3.1. I also have iCloud+ subscription. I want to take an advantage of iCloud Photos synchronisation capability, so you take a photograph on one device and it will automatically appear on another device.

At the moment, Photo Library is included in the iCloud backup for both devices.

Should I enable "Sync this iPhone" setting first and let it completely synchronise and then once it has done that then do the same on the iPad Pro? Or is it completely safe to enable it on both device and not worry about conflicts or any other possible issues?

[Re-Titled by Moderator]