To what extent is the common opinion valid, both religiously and scientifically, that delaying the husband's ejaculation into the wife's womb for two weeks after the first encounter is better, and that the mixing of semen with blood during the first intercourse causes uterine stickiness?

There is no harm for the husband in not practicing coitus interruptus (withdrawal) with his wife at any time; rather, that is the default. Coitus interruptus is only permissible with the mutual consent of both spouses. As for its medical effects, those should be inquired about from medical professionals.