Do you guys know when it would be the worst/busiest most crowded day during Spring festival, to get to the airport?

Usually should take less than one hour to get there, how long should add on top of that due to Spring festival?

I think they are asking people to check in 3 hours before international flights. Seeing as it is normally 2 hours, I would add an extra hour for all trips.

Getting to the airport should not take much longer, but getting through security checks and immigration/emigration will.

I'd suggest the bad days will begin on Friday, and get worse over the following 3 days.

Thanks for your answers, should then expect to find less people on the road from the 1st of February?

I suggest the bad days will be running up to Friday. Friday is CNY eve, and the eve is the big day for the families to get together and celebrate the NY together. Most will be aiming to get to hometown before that.
Saturday could be very quiet, as families will have been up late, and probably still full of alcohol.

February 1st and 2nd will be very busy with people travelling back to start work on the 3rd. Some people will also have taken a few days extra to take the following weekend. Those in a job that allows them to do this will have a car.

I have traveled in the middle of the holiday before, driven and flown, and it isn't too bad.

@ tiger: you're right, I got the dates wrong.

Saturday the roads out will be quiet, but I expect the tourist spots in and around the city, like Haigeng Daba and the parks could be busy, as for many Chinese it is a tradition to go for a family walk. Often walking up a mountain is required, and if I am right, Xi Shan could be hellish busy.