$ nasm -v
NASM version 2.13.02rc2 compiled on Sep 27 2017
$ cat test.asm 
org 0
times 4 times 16 db 0
%assign num $-$$
%warning num bytes used
db 0
$ nasm test.asm -l test.lst
test.asm:4: warning: 16 bytes used [-w+user]
$ cat test.lst
     1                                  org 0
     2 00000000 00<rept>                times 4 times 16 db 0
     3                                  %assign num $-$$
     4                                  %warning num bytes used
     4          ******************       warning: 16 bytes used [-w+user]
     5 00000010 00                      db 0
$ 

Expected: The doubled times should multiply its numbers.