[America/New_York]
TZ=EST5EDT,M3.2.0/2,M11.1.0
EST = designation for standard time when daylight saving is not in force
5 = offset in hours = 5 hours west of Greenwich meridian (i.e. behind UTC)
EDT = designation when daylight saving is in force (if omitted there is no daylight saving)
, = no offset number between code and comma, so default to one hour ahead for daylight saving
M3.2.0 = when daylight saving starts = the 0th day (Sunday) in the second week of month 3 (March)
/2, = the local time when the switch occurs = 2 a.m. in this case
M11.1.0 = when daylight saving ends = the 0th day (Sunday) in the first week of month 11 (November). No time is given here so the switch occurs at 02:00 local time.
So daylight saving starts on the second sunday in March and finishes on the first Sunday in November. The switch occurs at 02:00 local time in both cases. This is the default switch time, so the /2 isn't strictly needed.
[Europe/Paris]
TZ=CET-1CEST,M3.5.0/2,M10.5.0/3
CET = designation for standard time when daylight saving is not in force
-1 = offset in hours = negative so 1 hour east of Greenwich meridian
CEST = designation when daylight saving is in force ("Central European Summer Time")
, = no offset number between code and comma, so default to one hour ahead for daylight saving
M3.5.0 = when daylight saving starts = the last Sunday in March (the "5th" week means the last in the month)
/2, = the local time when the switch occurs = 2 a.m. in this case
M10.5.0 = when daylight saving ends = the last Sunday in October.
/3, = the local time when the switch occurs = 3 a.m. in this case
The European Union time zones are arranged so the switch takes place at the same time in all zones.
