help with time format

[Jen mlists]

hello list,

I saw these config lines in a name config-file,

@     1D IN      SOA     foo.com. admin.foo.com.  (
                                           2007071018 ; Serial
                                           1H         ; Refresh
                                           15M        ; Retry
                                           1W         ; Expire
                                           1D )       ; Minimum


The time format is in upper-case,but from what I saw in the bind
book,it should be low-case.For example,instead of '1H',it should be
written as '1h'.

Am I right?thanks.