Time covers the structuring, sequencing, duration, estimating and scheduling of activities and/or 
work packages, including the assignment of resources to activities, establishing project deadlines 
and monitoring and controlling their timely execution. These aspects should be displayed on a criti cal path diagram. 
 Project life-cycle models and their time-frames and phases are specific to different industries and 
businesses. For example, the models used in construc tion are different from those used in manu facturing or logistics. Similarly, the models used for R&D are different from those used for Supply 
Chain or for ICT (information and communication technology) support.
A project phase is a discrete time period of the project sequence, which is clearly separate from 
other periods. A project phase includes both major project deliverables and decisions which are the 
basis for the next phase. Phases have defined objectives and may have specified time limits. Differ ent phase models may be used for different kinds of (sub) projects which increases the complexity 
of their coordination. Milestones can be used to work towards specific targets or phase limits or 
intervals in between.
In practice the project phases can overlap (e.g. concurrent stages, fast-tracking). In programmes 
the phases normally apply to individual projects rather than to the programme itself. Portfolios are 
controlled by time intervals. There is usually an annual cycle of meetings and decision points for 
planning the portfolio for the coming year, perhaps with a forward view of several years, depending 
on the type of business or organisation. The portfolio will also have review points during the current 
delivery cycle to ensure that the overall portfolio of projects is on track, that resources are properly 
allocated and to allow remedial action to be taken when necessary. 
The aim of time scheduling is to determine what activities need to be carried out and when, and to 
put these activities into a logical sequence on a time line. Scheduling includes the interfaces between 
sub-projects and amongst work packages, as well as the duration and timing of activities. Time 
schedules depend on the relative priority of the work, the availability of resources with appropri ate skills and sometimes on culturally-dependent or weather-dependent seasons. Where there is 
uncertainty about the time-frame required for a particular phase or activity, a time ‘buffer’ or ‘float’ 
should be introduced into the schedule.