This page gives detailed information about the timezones used in Europe during the period and in the countries where TEE trains were running.

All countries used Middle European Time (one hour ahead of Greenwich Mean Time) as the standard time, but during the summer periods during these years Daylight Saving Time (DST, or Summertime) was introduced; which was two hours ahead of GMT. However, introduction was not simultaneously but graduately and starting/ending times became standardized only late in the period.

Italy was the first country that introduced DST in 1966. The periods until 1979 were as followed:

Note that during these years in most cases the DST period coincided with the summer timetables of the European railways. From 1980 Italy joined the other countries in their dates.

Spain was second to introduce DST in 1974. Periods were:

After that time the common rules were used.

France started in 1975:

In 1977 Belgium, Luxembourg and the Netherlands joined France with at that time a fixed rule: first Sunday in April until last Sunday in September. In 1981 this rule was replaced by: last Sunday in March until last Sunday in September (and is modified again in 1996). This rule was joined in 1978 by Spain (as told), in 1979 by Italy and Germany and in 1980 by Austria and Switzerland. Although Denmark had TEE trains running they were running during a period that no DST was used in Germany and Denmark.
Exact dates for the last period were:

Of course the dates from 1980 are not really relevant as these pages do not handle night trains.

Note: the periods are including the indicated last day!