Default [Q] How to schedule a regular auto back up ?

Hello,

I have set up the auto backup with Dropbox but my HTC m8 seems to be backing up the phone contents at random times or at least I can't make sense of its timing.

My current set up is to back up via wifi to my drop box account, I would like to have it do the back up at over night but sometimes it would back up at 8 pm when I am using the phone.

My question is : is there any way to specify the timing of the auto back ups ?

Thank you in advance!

Edit: sorry I just realized I posted in the wrong section, please move the thread. Thank you .