Presumably you've posted this thread in response to the previous one with the guy who'd belt went and took some valves and bits with it. In which case you should have already read the advice.
The belt on my A3 was changed at 79k (by previous owner). If i'd owned the car i would have changed it after 60k/5 years, whichever came first.
Audi have their advice but, as posts on here will testify, it could fail before that. If you have a full Audi service history then if it does go early and you are out warranty then you 'should' be protected (as the guy in the other thread was).
If i were you i'd change it at the next scheduled service (assuming that's within the next few months and you're not planning on piling 20k on the clock beforehand). Of course, if you favour independant specialists for servicing then you may want to consider getting it done even sooner.
People seem to panic a little about cam-belts. If you change them every 60k/5yrs then you really have nothing to worry about. If you have a full Audi service history then even in the event of a failure you should be covered by them.