Hi, I Am A Methadone Patient And My Employer Gives

Hi,
I am a methadone patient and my employer gives random drug tests I believe they are mouth swab tests. I screwed up and used heroin 5 days ago, was a stupid mistake and I haven't done it since. My question is will my saliva be clear after 5 days? And also if it does for whatever reason come up positive for opiates/morphine since this is what heroin metabolites into, can a positive results be explained off cause of my methadone? Or can they tell in mouth swab tests whether it's specifically methadone or heroin? Thank you