Wheel bearings defective – how long can you drive?

Hello, my bike bearing – I guess back right – is making increasing noises, since about 1,000 km. Since I have 1,500 km in front of me next week and small spare car, the following question: When should one change a bike bearing at the latest? Which signals should one pay attention to??? Thank you in advance for your answers! P. S: 138.000 km / Built. 07-2010