Tycho Brahe Mars oppositions

Hello,

I'm trying to validate the results of
a planet position algorithm for early
dates.

In the book "History of Astronomy",
by Anton Pannekoek, I found a little
table of times of Mars oppositions
in the period between 1580 and 1604,
which is reproduced below.

The table is based in the observations
by Tycho Brahe, and is very important
to the history of astronomy,
since it was used by Kepler to
discover his famous planet laws.

However, the book is not clear about
the dates and times.

- Are the dates in Gregorian calendar ?
( I know protestant countries were slow
to adopt the new calendar, by as much
as 100 years ! )

- What is the time zone he used
(or how can I convert the times to GMT) ?

Any help will be appreciated.

Regards
Omar

P.S. Mars Oppositions by T. Brahe
18/11/1580 01:31
28/12/1582 03:58
30/01/1585 19:14
06/03/1587 07:23
14/05/1589 06:23
08/06/1591 07:43
25/08/1593 17:27
31/10/1595 00:39
13/12/1597 15:44
18/01/1600 14:02
20/02/1602 14:13
28/03/1604 16:23