The TZ format is specified by POSIX, please refer to POSIX 1003.1 section 8.3
Example: 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 TZ format is specified by POSIX, please refer to POSIX 1003.1 section 8.3 Example: 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