The DST offset in seconds. Normally this is in the range of 0 to 3600 seconds (1 hour), but this field will accept any values in the int32 range to accommodate potential future legislation that does not fit with these assumptions.
The UTC time when the offset shall be applied.
The UTC time when the offset shall stop being applied. Providing a null value here indicates a permanent DST change. If this value is non-null the value shall be larger than the ValidStarting time.
See
MatterSpecification.v13.Core § 11.17.6.7