List all times in the day at a half hour rate
Pyth, 26 bytes
Pjbm%&quot;'%02d:%s0',&quot;d*U24&quot;03

Demonstration.
We start with the cartesian product of range(24) (U24) with the string &quot;03&quot;.
Then, we map these values to the appropriate string formating substitution (m%&quot;'%02d:%s0',&quot;d).
Then, the resultant strings are joined on the newline character (jb).
Finally, we remove the trailing comma (P) and print.