Re: What happens if two sperms bind onto an ovum at exactly the same time?

If more than one sperm fuses with an egg (referred to as polyspermy), 
extra mitotic spindles form which results in abnormal segregation of
chromosomes during cleavage, non-diploid cells are produced, and 
development quickly stops.  This illustrates why eggs have such 
effective blocks against fertilization by more than one sperm.
Information taken from "Molecular Biology of the Cell"
2nd edition, Bruce Alberts et al.