Yes, it will hold on to 2nd gear (not 3rd...) until 3100 RPMs or until your coolant level has reached 50 degrees C.
But I wouldn't recommend having to do that..... if I drive about 1/2 a mile it will usually shift out on it's own. I mean I try and avoid revving the engine that high when it's cold.
But I know it's not possible all the time.
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)