The positions specified are for the 1st day of the given month at about 9PM. This should apply to the whole month for all of the planets except perhaps Venus, which moves very quickly.
Month Venus Mars Jupiter Saturn Uranus Neptune Pluto Jan Oph M Cap Tau Lib Psc Aqr Sgr Feb Cap M Aqr Tau Lib Psc Aqr Sgr Mar Aqr O Aqr Tau Lib Cet Aqr Sgr Apr Psc O Psc Tau Lib Psc Aqr Sgr May Ari E Ari Tau Lib Psc Aqr Sgr Jun Tau E Tau Tau Vir Psc Aqr Sgr Jul Cnc E Tau Gem Vir Psc Aqr Sgr Aug Leo E Gem Gem Vir Psc Aqr Sgr Sep Vir E Cnc Gem Lib Psc Aqr Sgr Oct Lib E Leo Gem Lib Psc Aqr Sgr Nov Sgr E Leo Gem Lib Psc Aqr Sgr Dec Sgr E Vir Gem Lib Psc Aqr Sgr
Venus is only visible just before the Sun rises or just after it sets. The letter after Venus' constellation refers to when it is visible.
When a planet is on the opposite side of the sky from the Sun from our point of view, it is called opposition. When a planet is at opposition, it is usually at its closest point to the Earth. Since Venus and Mercury are inner planets, they can never be at opposition from our point of view. Mars typically goes into opposition every 25 to 26 months.
Mars does not go into opposition in 2013