Why is GVim displaying the output from system() function as ^M and ^@

Why is GVim displaying the output from system() function as ^M and ^@

function! g:insert_date()
let l:pattern="\\d\\{2}:\\d\\{2}"
let l:match=match(getline('.'),l:pattern)
let l:curline=getline('.')
echo "Current line: ". l:curline
normal gg
let l:time=system("time /t")
let l:date=system("date /t")
let l:date_time=l:date."\t".l:time
if l:match!=-1
echo match
normal dd
"call setline('.',system('time /t')."<<>>")
call setline('.',l:date_time)
else
echo match ." ". l:curline." ".l:pattern
sleep 2
normal O
"call setline('.',system("time /t")."\r")
call setline('.',l:date_time)
normal dd
endif
endfunction
I have this code above that is supposed to insert the date and time in the
first line of the file.
I was going to assign it to a BufRead autocommand but it's not perfect,
yet. Basically, it checks if there is a time string in the first line of
the file and if found it updates it. If not, it opens a newline above and
inserts the date. The problem is that it does not open a newline when the
string is not found. normal 0 is the culprit. It works when I type it in
the command line but fails when the function is called. Also, I don't why
you have to escape the regExp twice in the script while it works fine with
one backslash with ? and /.

As you can see, I have commented the line with the system() function
because it keeps inserting visible null bytes(ascii 0) and carriage
returns(ascii 13). What is system() doing that makes them visible. I
haven't found a workaround for this( read! does not store in a variable. I
need the date and time in
one line).
call setline('.',system("time /t")."\r")
call setline('.',system("time /t")."\n\n\n\n\n") ^@^@^@^@^@^@^@
call setline('.',system("time /t")."\n\n\n\n\n") ^@^@^@^@^@^@^@ (0)
call setline('.',system('time /t')."\r\r\r\r\r\r") ^M^M^M^M (13)
read! time\ /t
Additional details:

encoding=utf-8
set list is off
Font is consolas:h10
file format is dos
version=7.3