Setting up my vimrc

I'm a beginner and newbie to vim.
I was just going to ask about how to set up my vimrc to backup files
to a directory that is depended on the date with a file extension that
is dependent on the time
This is the current contents of my vimrc.

:set nocompatible
:set autoindent
:set history=300
:set ruler
:set incsearch
:syntax enable
:filetype on
:set so=4
:set patchmode=.orig
:set backup
:let &backupdir="/home/adam/Shortcuts/Backups/" . strftime("%y%m%d")
:let &backupext=strftime("%H%M%S") . ".bak"

I was guided to use :let &back... by some good folks on the IRC
channel...
whenever I try to do it, though, I get "E510: Can't make backup file
(use ! to override)`
I'm sure you can understand from what I've got here what I want it to
do. Please help me.
how do i get it to do what I want?

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