Collaborations imply interdisciplinary work, and require exchanges, communication and compromise. When managing a project, collaboration will lead to complex interactions and feedback between tasks. The planning and scheduling phase of a project already benefits from a large number of tools, mostly based on the Precedence Di- agramming Methods (PDM) and its precedence links. This linear vision of how a project shall be planned and sched- uled does not fit with the consequences of collaborative work, and unfortunately, no mainstream method for project planning and scheduling does. This work proposes a collaborative planning and scheduling framework based on gathering and handling of temporal constraints through a qualitative temporal algebra, and then on matrix based task-sequence optimization. It provides equal treatment to all constraints, highlights conflicts and propagates the effect of a constraint modification into the existing plan, thus taking coupling, feedback and rework into account.