For how long can stock options be exercised?

You realise that shares in a startup are illiquid (not readily sellable) and that options are only a right to acquire (ie PAY at pre-determined price) for those shares? In general they represent the difference between the (sometimes raman noodle) pay and market salary from working at a pure cash compensated company so the cliff represents the initial work. Thus you would only ever cash out when the company gets sold or an existing shareholder makes you an offer under any pre-existing agreement. The question is are you willing to "salary sacrifice" and bet that the business skills of the founders is enough to grow the value of your options faster than if you took straight cash immediately? (eg as contractor). Also check the good/bad leaver provisions.