Hallo Steffen,

> How can I find the opposition (Conjunction) time of a planet with Guide?

a simple, perhaps not quite exact solution: right klick on the planet,
from the menu use animation, make ephemries (Ephemeride
erstellen), set step size to 1 day and make sure that in options the
elongation and illuminated fraction is marked. Now look for the day
where the elongation has it's maximum (near 180 deg, opposition
date) for the outer planets or where the elongation is minimal (near 0
deg and illumination near 0% (untere Konjunktion) or 100% (obere
Konjunktion)) for Venus and Mercury.

Clear skies
Bernd


Bernd Brinkmann

Sternwarte Herne, #A18
Herne, Germany

e-mail: info@...
http://www.sternwarte-herne.de