As you may know, Mojang has recently implemented username changes for Minecraft accounts. However, here on QC, some of our plugins don't fully support username changing quite yet.
If you don't want your Ontime to reset, to have issues with your chests and such, and probably a myriad of other things, don't change your username yet.
We're confident we can recover Ontime/chest permissions for anyone who has already changed theirs, and we're working as hard as we can to fix all of this.
If you have already changed your username, an Op should be able to help unlock your things. It might take a while to find a free one, though.
If you haven't yet changed your username, but want to, you can use /cpersist and /unlock to go around your home and unlock your things, change your name, then go around and use /lock to lock everything again.