I have tested the Seconds Calculators under 5 different browsers:
Microsoft Internet Explorer
As of my Seconds Calculators release 1.1.000, the automatic daylight / standard timezone adjustment in the post-submit calculations 3, 4, 5, and 6 no longer depends upon your browser's built-in logic for daylight / standard times for American timezones. So daylight / standard logic should work OK in browsers released before the new (2007) daylight saving rules. For more on time zones and rules governing daylight / standard times, see the timezone notes page.