iPhone 5 64GB | How Long Did It Take: When You Erased All Contents and Settings to Prepare for the Batter or Button Replacement

Hi. For those who've erased all contents and setting before they had their iPhone 5 64GB's (iOS 8.1) battery and/or button replaced (free from Apple if the unit qualifies), how long did it take for it to be all erased?

Or there really no need to erase all contents and setting because you can rely on passcode (maybe setting it to more than 4 digits) to prepare it for this replacement program? What's the best way to go about it?

Thank you in advance.

God bless, Rev. 21:4