We have measured magnetic fields up to $17.7\mathrm{T}$ with a rise time of $75\mathrm{ns}$ using temporally resolved Faraday rotation of a single longitudinal mode laser beam through a magneto-optically active bulk waveguide. We believe this to be the first time that such large, rapidly varying magnetic fields have been measured with this class of materials (multicomponent terbium borate glass). As there was no measurable lag between the magnetic field inferred from the angle of rotation of the laser beam and the electromagnetically measured field, our sample of terbium borate glass has a spin-lattice relaxation time of a few tens of nanoseconds at most at approximately room temperature $\left(300\mathrm{K}\right)$ . The highest peak magnetic fields were measured in wire-array Z-pinch experiments on a $0.5\mathrm{MA}$ pulsed power machine.