The Sun spends about 30 days in each sign.
The Moon spends about 2 1/2 days in each sign.
Mercury spends about 14 to 30 days in each sign.
Venus spends between about 23 days to a little over 2 months in a sign.  
Mars stays in one sign for about 1.5 months.
Jupiter stays in one sign an average of one year.
Saturn stays in one sign for about 2 1/2 years.
Uranus stays in one sign about 7 years.
Neptune stays in each sign about 14 years.
Pluto stays in each sign between 14 and 30 years.

Mercury Retrograde thru the signs
Mercury Retrograde De Mystified