TZ

set/export TZ=EST

test.rb
puts File.open('aaa.txt') {|f| f.mtime }
puts File.open('aaa.txt') {|f| f.mtime }.zone
puts File.open('aaa.txt') {|f| f.mtime }.utc_offset
puts Time.now.utc_offset
puts Time.at(0).utc_offset

ENV["TZ"] = "CET"
puts File.open('aaa.txt') {|f| f.mtime }
puts File.open('aaa.txt') {|f| f.mtime }.zone
puts File.open('aaa.txt') {|f| f.mtime }.utc_offset
puts Time.now.utc_offset
puts Time.at(0).utc_offset



linux
2021-06-14 17:53:10 -0500
EST
-18000
-18000
-18000
2021-06-15 00:53:10 +0200
CEST
7200
7200
3600



windows
cruby 2.7
2021-06-15 00:57:09 +0100
eri
3600
3600
0
2021-06-14 23:57:09 +0000
CET
0
0
0

without fix
2021-06-15 01:57:09 +0200
SELČ
7200
0
0
2021-06-15 01:57:09 +0200
SELČ
7200
7200
3600

with fix
2021-06-14 23:57:09 UTC
UTC
0
0
0
2021-06-15 01:57:09 +0200
CEST
7200
7200
3600