Saliva Test (swab drug test) How long can I not eat/drink/smoke before test?

I have a swab test on Monday at 2:30 and I am wondering how long do I have to wait to eat/drink/smoke cigarettes before the test? I am going to the dentist a couple hours before hand and then have about a 2 hour drive back to my city for my test. Is that enough time for not drinking water? Since I will be at the dentist with water in my mouth 2 hours prior? Also can I smoke cigarettes before the test? If so do you know the cut off time? Thank-you! I just don’t want to have my test be invalid! Really looking forward to this job!