In LYNX, each project receives a Scheduled Start date calculated by the scheduling engine. This date may apply to projects with the status "Not Started" or "Released."

A Scheduled Start date can be:

• Today: positioned at the Green Line
• Later than today (i.e., postponed): positioned after the Green Line

This article explains scenarios where the Scheduled Start date is postponed to a future date.

Introduction

Understanding LYNX Scheduling Logic

LYNX supports both forward scheduling (As Soon As Possible - ASAP) and backward scheduling (Just-In-Time - JIT). The scheduling engine applies several principles to maintain project flow:

• Maintain continuity of the Critical Chain - tasks must be connected without gaps to ensure optimal flow.
• Minimize Work-In-Progress (WIP) -  tasks start only when necessary, avoiding premature execution.
• Avoid idle time - scheduling aims to eliminate waiting periods between tasks.

Note: the same scheduling logic applies, when a project is calculated in "Debuffered" mode

Why the Scheduled Start Might Be Postponed

Postponement can occur for the following reasons:

1. Backward Scheduling Logic: If a project is scheduled backwards from a fixed end date, the system calculates the Scheduled Start as:
   End Date - Critical Chain Duration.
   If there's a time gap between today and the calculated start, the project is effectively postponed.

2. Non-Working Days: Tasks on the Critical Chain might span vacation periods or non-working days for assigned resources, increasing the duration and pushing the start date.

3. Start-No-Earlier-Than (SNET) Constraints: If a task on the Critical Chain has a constraint that prevents it from starting before a certain date, the project’s start may be delayed accordingly.

This article focuses on reasons #2 and #3.

Examples

Baseline

The project in this example has a Critical Chain of 35 days, including Task 1 adding 25 days and Task 2 adding 10 days.  Other characteristics are:

• Duration of Task 1 is 25 days, however the estimate is only 20 days. 
• As Jack is on vacation for 5 days during Task 1, 5 Non working days are added to the duration of Task 1
• Scheduled Start is Today (21st of April) - positioned at the "Green Line"

Note: if the Vacation of Jack Morgan would start at 21st of April, the project obviously can only start when he is back.  And in this case the "Scheduled Start" would move to Monday 26th of April. 

Postponement Scheduled Start, triggered by Non-working days

In the example below, also Tom Smith will also be on leave for 4 days. This extends the Critical Chain to 39 days, as the required duration for Task 2 increases from 10 to 14 days. 

Other characteristics are:

• Task 2 spans the leave period of Tom (from 2nd of June - 5th of June), scheduling 5 days before and 5 days after his leave
• The total Non working days for the project increases to 9 days
• Buffer Consumptions increases with 4 days
• Scheduled Start is still "Today" (21st of April)

What if leave of Tom starts 1 weeks sooner?

If Tom’s leave starts one week earlier, this creates a gap in the Critical Chain when starting on 21st of April. To preserve task connectivity and comply with scheduling rules, the system:

• Postpones the Scheduled Start by 4 days
• Ensures continuous flow without idle time

Starting the project earlier would not speed it up and would instead introduce a waiting period.

Postponement Scheduled Start, triggered by a SNET Constraint

If Task 2 has a SNET (Start Not Earlier Than) constraint - e.g., cannot start before 2nd of June 2025:

• The Critical Chain cannot begin until that date.
• The Scheduled Start of the entire project is automatically postponed by 5 days to preserve flow.

Summary

LYNX postpones a project's Scheduled Start only when it is necessary to:

• Preserve the integrity of the Critical Chain
• Avoid gaps or idle time
• Respect resource availability and task constraints

These intelligent adjustments ensure the most efficient and realistic schedule, while minimizing unnecessary Work-in-Progress.