Constraint set &1 has no time constraints assigned to it

What causes this issue?

There is no valid time constraint assigned to the constraint set.

System Response

Constraint sets without time constraints may affect the performance of
the system.

How to fix this error?

Assign valid time constraints to the constraint set or delete the
constraint set if you do not need it (see
<DS:SIMG./SCMTMS/VC_PLN_OPT_C>Define Scheduling Constraints</>).

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.