The patch below proposes an extension for and resolves 3 bugs 
of xclock 1.0.3.  I think the code and comments should be 
self-explanatory, but if there are questions just ask and I 
will describe the underlying logic.  

Summary--

extension: clock_tic()
   The update period is used to round the next display time.  Thus e.g. 
   a value of 15 s results in redisplays at :00 :15 :30 :45 :00 ...

bug 1: Initialize ()
   if XRENDER && w->clock.render && !defined(NO_I18N) && !no_locale 
   then the already computed min_width is overwritten by the plain 
   font rule: min_width = XTextWidth(w->clock.font, str, len) + ... 
   The new behaviour conforms to xclock 1.0.2.  

   reproduce: xclock -d -utime -fn 10x20  (notice the wide window)

bug 2: RenderTextBounds ()
   The offset off is relative to str[0..off..len-1] and can't be used 
   for utf8_str due to multibyte characters.  This patch calls 
   clock_to_utf8() first for the head and then for the tail. 

bug 3: clock_tic()
   if(!w->clock.utf8) && defined(HAVE_ICONV)
   then the head to skip is taken into account by 
   utf8_str = clock_to_utf8(time_ptr + i, len - i) 
   so there is no need for 'strlen(utf8_str) - i' afterwards.