Oder vollständig aus dem Manual (allerdings aus dem BT200 nicht aus dem GXP)
This parameter controls whether the displayed time will be daylight savings time or not. If set to “Yes” and the Optional Rule is empty, then the displayed time will be 1 hour ahead of normal time. The “Automatic Daylight Saving Time Rule” shall have the following syntax: start-time;end-time;saving
Both start-time and end-time have the same syntax:
month,day,weekday,hour,minute
month: 1,2,3,..,12 (for Jan, Feb, .., Dec)
day: [+|-]1,2,3,..,31
weekday: 1, 2, 3, .., 7 (for Mon, Tue, .., Sun), or 0 which means the daylight
saving rule is not based on week days but based on the day of the month.
hour: hour (0-23), minute: minute (0-59)
If “weekday” is 0, it means the date to start or end daylight saving is at exactly the given date. In that case, the “day” value must not be negative. If “weekday” is not zero and “day” is positive, then the daylight saving starts on the first “day”th iteration of the weekday (1st Sunday, 3rd Tuesday etc). If “weekday” us not zero and “day” is negative, then the daylight saving starts on the last “day”th iteration of the weekday (last Sunday, 3rd last Tuesday etc). The saving is in the unit of minutes. The saving time may also be preceded by a negative (-) sign if subtraction is desired instead of addition. The default value for “Automatic Daylight Saving Time Rule” shall be set to
“04,01,7,02,00;10,-1,7,02,00;60” which is the rule for US.
http://www.grandstream.com/pdf/BT200UserManual.pdf
