Nope. Some people think that an orgasm of the female can cause the cervix to "dip" into a puddle of semen which could enhance delivery of the sperm to the fallopian tubes. But in your scenario, sperm have already been delivered and one of them has penetrated the egg. Orgasm is unlikely to make any difference. On the the other hand, I don't think it will hurt!
No. Sex/orgasm during probable implantation will not reduce preg chances. Although there are uteri contractions during orgasm, their brief nature and the fact that implantation is a dynamic process makes prgasm unlikely to affect it. No studies show that implantation will be hampered.