The system NdGa-H2 shows intriguing hydrogenation behaviour with various intermediate phases. Gallium chains of the Zintl phase NdGa are fragmented by inserting hydrogen leading to (GaH)2- chains with partially occupied hydrogen positions as evidenced by ex situ neutron powder diffraction on deuterated samples. Full occupation leading to electron precise Nd3+H-(GaH)2- could not be achieved as yet, probably due to high desorption pressure. These Zintl phase hydrides are difficult to prepare and characterize by ex situ diffraction methods. Therefore time-resolved in situ neutron diffraction shall be applied to study these transient phases, determine their crystal structures and elucidate reaction pathways. In the case of NdGaH1+x (0 ≤ x ≤ 1) they further offer the possibility of attaining the fully hydrogenated phase with x = 1, which is elusive so far. A user supplied single-crystal based sapphire gas pressure cell will be used to collect neutron powder diffraction data with a time resolution of two minutes, thus mapping the complete deuteration reaction pathway of NdGa.