Can a girl get pregnant if guy is only in her for 5 seconds and she starts period day later?

No, it is not possible for a girl to get pregnant if the guy is only in her for 5 seconds and she starts her period a day later. For pregnancy to occur, the sperm must travel through the vagina and cervix and reach the fallopian tube, where it can fertilize an egg. This process usually takes several minutes, and it is not possible for sperm to reach the egg if the man is only inside for 5 seconds.

Additionally, if a woman starts her period, it means that she is not ovulating, and pregnancy cannot occur during this time.