MnBi₂Te₄ is a layered magnetic material which has been under intense study in recent years. It combines strong in-plane ferromagnetism with weaker out-of-plane antiferromagnetism, effectively becoming a one-dimensional antiferromagnet. Mechanical exfoliation allows study of ultrathin (<10 layers) samples, allowing a wide variety of experimental tests. We present measurements of the ultrafast magnetization dynamics using pump-probe techniques across varying thicknesses, showing both slow thermally driven behaviours and magnon oscillations characteristic of such a material. Our results also highlight the apparent limitations of the current theoretical models, suggesting some need for improvements our understanding of the magnetic interactions.