Is a gonorrhea and chlamydia test reliable 2.5 days post exposure ?

Test: depends on kind of test but generally yes

Maybe. Maybe not.: The test is just a test and doesn't care when the exposure was. The real question is, "What does the result mean?" Only then does the timing become very important. A positive is a positive (usually), but at merely 2.5 days, a negative might be a false negative. Take a look at: http://www.ndhealth.gov/hiv/Docs/CTR/TimePeriodsReference_HIVSTDsHep.pdf