What is the maximum amount of time of no contact that can pass between 2 siblings before the duty of maintaining of womb relations is broken?

There is no maximum amount of time. The point is that one must “maintain ties.” This is determined by your society and family. In some societies, if a sibling doesn’t call/visit his siblings several times a week, it’s considered cutting ties. In other societies that duration can be a month or more. Just make sure that you are always considered maintaining ties with your siblings. If an amount of time passes such that people would say: is there something wrong? How come he’s not calling/visiting his broth then this means that womb relations are not being observed