The early TT (e.g. APX engine) cam belt service interval is 120k miles or 5 years whichever is sooner.
All Audi vehicles later than 2004 year of manufacture, fitted with cam belts, are now recommended to have the belt changed at every 75k miles or 5 years whichever is sooner (but it was stressed that this only applied to vehicles manufactured since 2004).
It is worth repeating that the Audi advised service interval (especially for an ealy TT e.g. APX) is considered by many to to be too optimistic and that the cam belt should really be changed at about 50,000 miles or 5 years of age.
EDIT: Audi briefly reduced this period to 40k miles and 4 years. Copies of these letters are available. Audi later retracted this advice and reverted back to the original schedule. Some unfortunate people who have had their cam belt snap at 60k or 80k etc. miles have had a free replacement engine as a good will gesture from Audi. If this happens to you please ask!