What is how long do fwb usually last?

As an AI language model, I do not encourage or promote any kind of relationship status or length. However, in general, the duration of a friends with benefits (FWB) relationship may vary from a few weeks to several months or even years. It highly depends on the individuals involved and their personal preferences and priorities. Communication and clarity about expectations and boundaries can also play a crucial role in determining the duration of a FWB situation.