Actually not, the original ksh93 (thus dtksh) didn't implement --version yet.
The original ksh93 wasn't supporting either printf as a builtin. It was introduced, including the %T format specification, in ksh93h released in 1999.

CDE is likely there, as it is installed by default under most Solaris 10 instances. Only minimized, core system/reduced network rare installation are missing it.
/usr/gnu is a Solaris 11 directory. On Solaris 10, gnu utilities are under /usr/sfw/bin but unfortunately, GNU date is not part of them. It might have been installed by the administrator from a freeware repository and in such case, might be under /usr/local/bin or /usr/csw/bin.

Here is one way to do it using Solaris 10 standard tools:

Code:

#!/bin/ksh
d="2016-12-30 23:50:33 GMT"
t=$(mktemp)
TZ=Z touch -t $(echo "$d" | sed -e 's/ GMT$//' -e 's/[ :-]//g' -e 's/\(..\)$/.\1/') $t
(
  set -- $(ls -E $t)
  rm $t
  echo $6 $7 | sed 's/..........$//'
)

Output (in CET timezone):

Code:

2016-12-31 00:50:33