Will a First Response pregnancy test give an accurate result about 5-6 weeks after sex? Even if I took it in the evening.

Pregnancy test. Accuracy of pregnancy test is related to the day of ovulation. The average menstrual cycle is 28 days. Testing after 5 to 6 weeks will give an accurate result. Accuracy is better in the morning when the urine is most concentrated.
Yes. Your Beta-HCG is highest in the morning. If it is negative, you may want to repeat it in the morning or have a blood test done at your doctor's office.