I use 7 psi pressure 10-12hg vac I do not time it..I just walk away and go make a call or make a sandwich etc...I forget or get pulled away and wander back after an hour or the next morning lol I use this stuff to find small leaks and smoke to find larger ones
https://www.amazon.com/dp/B082MQZBV...mp=&crid=1AK9740X81MGY&=&sprefix=micro+lea
https://www.amazon.com/dp/B082MQZBV...mp=&crid=1AK9740X81MGY&=&sprefix=micro+lea