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