I took azithromycin in one big dose of 1g to cure nsu, how long before the medicine should have cleared the bacteria as I just had sex after 6 days?

Should be OK. It is usually recommended to avoid sex for a week and until symptoms are completely gone, and 6 days is a bit early. However, azithromycin is very long acting; it remains in the system for almost 2 weeks after a single dose. So it is very unlikely you would be able to infect a partner. However, best to discuss with the doctor or clinic where you were treated.