An important aspect of the propagation delay in blockchain networks is the block verification time, which is also responsible for the so-called verifier's dilemma. Models for the block verification time can help to understand and improve the verification process. Moreover, modeling the verification time is necessary for blockchain network simulations. In this paper, we present JOIST, a new model for the block verification time of Zcash. We identify computationally complex operations in the verification process of Zcash, and derive our model based on characteristic transaction features. We evaluate JOIST and show that the model is consistently more accurate than existing models, which consider the block size only.