$ cat test_script.sql 
set names utf8;
select version();
select @a:=time('1:11'), charset(time('1:11')), charset(@a), collation(@a);
select @a:=sec_to_time(1), charset(sec_to_time(1)), charset(@a), collation(@a);
select @a:=date('11-01-01'), charset(date('11-01-01')), charset(@a), collation(@a);
select @a:=from_unixtime(1), charset(from_unixtime(1)), charset(@a), collation(@a);
select @a:=time('1:11'), @a < time('2:22');
$ 
$ mysql -t < test_script.sql 
+-----------+
| version() |
+-----------+
| 5.5.11    |
+-----------+
+------------------+-----------------------+-------------+-----------------+
| @a:=time('1:11') | charset(time('1:11')) | charset(@a) | collation(@a)   |
+------------------+-----------------------+-------------+-----------------+
| 01:11:00         | binary                | utf8        | utf8_general_ci |
+------------------+-----------------------+-------------+-----------------+
+--------------------+-------------------------+-------------+-----------------+
| @a:=sec_to_time(1) | charset(sec_to_time(1)) | charset(@a) | collation(@a)   |
+--------------------+-------------------------+-------------+-----------------+
| 00:00:01           | binary                  | utf8        | utf8_general_ci |
+--------------------+-------------------------+-------------+-----------------+
+----------------------+---------------------------+-------------+-----------------+
| @a:=date('11-01-01') | charset(date('11-01-01')) | charset(@a) | collation(@a)   |
+----------------------+---------------------------+-------------+-----------------+
| 2011-01-01           | binary                    | utf8        | utf8_general_ci |
+----------------------+---------------------------+-------------+-----------------+
+----------------------+---------------------------+-------------+-----------------+
| @a:=from_unixtime(1) | charset(from_unixtime(1)) | charset(@a) | collation(@a)   |
+----------------------+---------------------------+-------------+-----------------+
| 1969-12-31 19:00:01  | binary                    | utf8        | utf8_general_ci |
+----------------------+---------------------------+-------------+-----------------+
ERROR 1267 (HY000) at line 7: Illegal mix of collations (utf8_general_ci,IMPLICIT) and (latin1_swedish_ci,NUMERIC) for operation '<'
$ 
$ # I changed server versions here
$
$ mysql -t < test_script.sql 
+-----------+
| version() |
+-----------+
| 5.1.57    |
+-----------+
+------------------+-----------------------+-------------+---------------+
| @a:=time('1:11') | charset(time('1:11')) | charset(@a) | collation(@a) |
+------------------+-----------------------+-------------+---------------+
| 01:11:00         | binary                | binary      | binary        |
+------------------+-----------------------+-------------+---------------+
+--------------------+-------------------------+-------------+---------------+
| @a:=sec_to_time(1) | charset(sec_to_time(1)) | charset(@a) | collation(@a) |
+--------------------+-------------------------+-------------+---------------+
| 00:00:01           | binary                  | binary      | binary        |
+--------------------+-------------------------+-------------+---------------+
+----------------------+---------------------------+-------------+---------------+
| @a:=date('11-01-01') | charset(date('11-01-01')) | charset(@a) | collation(@a) |
+----------------------+---------------------------+-------------+---------------+
| 2011-01-01           | binary                    | binary      | binary        |
+----------------------+---------------------------+-------------+---------------+
+----------------------+---------------------------+-------------+---------------+
| @a:=from_unixtime(1) | charset(from_unixtime(1)) | charset(@a) | collation(@a) |
+----------------------+---------------------------+-------------+---------------+
| 1969-12-31 19:00:01  | binary                    | binary      | binary        |
+----------------------+---------------------------+-------------+---------------+
+------------------+-------------------+
| @a:=time('1:11') | @a < time('2:22') |
+------------------+-------------------+
| 01:11:00         |                 1 |
+------------------+-------------------+
$