  Quantum emitters in hexagonal boron nitride (hBN) have recently emerged as
promising bright single photon sources. In this letter we investigate in
details their optical properties at cryogenic temperatures. In particular, we
perform temperature resolved photoluminescence studies and measure photon
coherence times from the hBN emitters. The obtained value of 81(1) ps
translates to a width of $\sim$12 GHz which is higher than the Fourier
transform limited value of $\sim$32 MHz. To account for the photodynamics of
the emitter, we perform ultrafast spectral diffusion measurements that
partially account for the coherence times. Our results provide important
insight into the relaxation processes in quantum emitters in hBN which is
mandatory to evaluate their applicability for quantum information processing.
