No, there is no other option to sort the files based on datetime.
If you are using hadoop version < 2.7, you will have to use sort -k6,7 as you are doing:
hdfs dfs -ls /tmp | sort -k6,7
And for hadoop 2.7.x ls command , there are following options available :
Usage: hadoop fs -ls [-d] [-h] [-R] [-t] [-S] [-r] [-u] <args>
-d: Directories are listed as plain files.
-h: Format file sizes in a human-readable fashion (eg 64.0m instead of 67108864).
-R: Recursively list subdirectories encountered.
-t: Sort output by modification time (most recent first).
-S: Sort output by file size.
-r: Reverse the sort order.
-u: Use access time rather than modification time for display and sorting.
So you can easily sort the files:
hdfs dfs -ls -t -R (-r) /tmp
Hope this will answer your query to some extent.