I'm dealing with a bunch of stock market tick data files, one file per
trading day, going from 4-Apr-2008 to present. Each file has around
800,000 records. All timestamps are GMT.

I am trying to adjust GMT to Eastern Time, USA, and further, need to
take into account Daylight Savings Time (DST) vs Standard Time (ST)

Two questions:

1. Does GMT "change"? (ie, does it change by 1 hour for DST vs ST)

2. I understand that British Summertime (BST) changes about a week
differently than DST, but, if GMT is "static" (ie, no changes), then I
probably don't need to worry about BST vs DST, right?

Spoo