This achievement is not as hard as it sounds. For this you will need to learn to maximize your challenges. Instead of just taking headshots, do a headshot in slow-motion while in active cover. Use grenades when enemies are clumped together. When fighting a Phase Caster don't kill him too quickly, they summon enemies that can help you work on more kill challenges. Every body you make a psychic link with also counts as a challenge, so if you can link 10 bodies in one interval that's 10 challenges right there. Once you learn the best way to maximize your challenges, getting 30+ in any interval is easy.
See "Completionist" for additional details.