If music is an art of time, what kind of time is it? And is it possible to share this musical time between man and machine? These questions, which may seem abstract, become very tangible and pressing in mixed music where a computer must produce electronic sounds alongside human musicians. This presentation will focus on clarifying these questions and providing elements of answers based on the experiences with the Antescofo system, a computer system that allows the composer to define an electronic answer and to realize it taking into account the performer's musical interpretation during the concert.