Define New Time Zones

You may want to define new time zones. For instance, Canada has decided to follow the U.S. standard, while Mexico has decided to stay with the older definition. This means that for several weeks each year, PST in Los Angeles will be different from PST in Tijuana.

You can define a new time zone, such as PSTM (for PST Mexico) with the older DST ID, to distinguish it from the PST (for PST U.S. and Canada) with the new DST ID.

See Understanding Time Zones.

After defining your new time zones, run Generate Query Offsets again so that the offsets include the new time zones.