Generating off line a plan of activities before executing it on line is no longer realistic when one expects disturbances from an uncertain environment. Focusing on temporal plans and uncertain temporal constraints, we will show that there are three main ways of tackling the issue: the reactive way, the proactive way and the progressive way, which will be illustrated through existing models and systems. In realistic applications, one usually needs all of them, requiring a unified model. Such a model will be introduced together with the first results of a modular system developped in the ILOG programming environment.