UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.79 Safari/537.36

Steps to reproduce the problem:
1. var date = new Date(-25569*86400000) //in Chinese locale time zone.
2. console.log(date.getTimezoneOffset());
3. console.log(date.toLocaleString());

Result: 
-485
"Sat Dec 30 1899 08:05:43 GMT+0805 (China Standard Time)"

What is the expected behavior?
the getTimezoneOffset should return -485-43/60 = -485.283333
Or
the date should be:
Sat Dec 30 1899 08:05:00 GMT+0805 (China Standard Time)

What went wrong?
If the time zone offset is 08:05:43, why the getTimezoneOffset return only -485?

The return value should be -485-43/60 = -485.283333.

If current getTimezoneOffset is correct that means another bug,
the Date should be 
Sat Dec 30 1899 08:05:00 GMT+0805 (China Standard Time).

43 seconds is needless.

Please help to check.

Did this work before? Yes Chrome v66

Chrome version: 67.0.3396.79  Channel: stable
OS Version: OS X 10.13.5
Flash Version: 

Please check it carefully, it relates to our OADate calculate system.