What is the number of iteration needed for the message passing algorithm to converge when applied to a tanner graph (factor graph)?

Question

I understand that the message passing algorithm (Belief Propagation algorithm), when applied to a factor graph, (tanner graph, bipartite graph) consists in an exchange in messages between the factor nodes and the variable nodes, these messages keep being updated until a certain number of iterations where we reach convergence. And here is my question: What is the number of iterations needed for the message passing algorithm to converge when applied to a tanner graph (factor graph)? Is there some conditions for the convergence to happen? if yes, what are these conditions? I am not using a loopy graph, my graph is very simple, it is an acyclic bipartite graph, tanner graph. Thanks in advance!