Took abouit 1.5/2.0 hrs. Just wanted to take my time and do it right. I don't know about all the other Mercedes out there, but changing the fluid on a 94C280 is a piece of cake. Got a new filter and pan seal for about $30 online. Changed to Mobil 1 Syn for about $56 and when I went for a test ride after I was done, I noticed the shifting was much smoother right away.
PS: When checking the pan for metal particals, I found only 1 small speck. Not bad for 160,000 miles