I assume this is what you want:
update tbl set `Time` =
ADDDATE('1970-01-01 17:00:00', INTERVAL 8*((`ID`-1) DIV 2) MINUTE);
Producing (for a table already having rows ID1~6):
mysql> select * from tbl;
+------+----------+
| ID | Time |
+------+----------+
| 1 | 17:00:00 |
| 2 | 17:00:00 |
| 3 | 17:08:00 |
| 4 | 17:08:00 |
| 5 | 17:16:00 |
| 6 | 17:16:00 |
+------+----------+
6 rows in set (0.00 sec)