Alcohol may be metabolized at 1 oz of ETOH per hour but ETG which is synthesized by the liver in the breakdown of alcohol is present in the urine for 3 to 5 days (sometimes as far out as 7 days) so the answer to your question of weather you can drink on Friday and test positive on Monday is Yes. If you slipped so be it get back on your program. If you had to test after drinking on Friday you will most likely test positive on Monday - It's best not to try to figure out what you can get away with and just not drink - easier said than done I know (believe me I know) But you will never win with this strategy.
Peace and Namaste
Hppy