Is it right to do hCG blood test at the 5th day before the menses time?

Why not wait? If a normal regular period comes, then a woman is not pregnant. There is rarely a reason to test sooner (and patience is a valuable trait to nurture, for parents who'll be raising children). If periods are unpredictable, then a urine pregnancy test is accurate 2-3 weeks after sex (when conception might have happened).