Roof rats are the worst rodent pest in the state of Florida and most abundant. The Norway rat (Rattus norvegicus) that is familiar to most people is rare in Florida. Roof rats consume and destroy stored animal and human food, attack fruit crops, and take up residence in attics, soffits, hollow walls, and out-buildings.
1 The sperm brings in another 23 chromosomes to complement the 23 held in the egg to get to a total of 46 chromosomes - what all of us normal people have.  We know from in vitro fertilization studies that the egg is only capable of being fertilized for about 24 hours after ovulation.
The time sperm remains viable in the oviduct or infundibulum is not precisely known and it is probably variable. However, in other species the viability of sperm drops off after about 10 to 15 days. Generally it is believed that the effective mating takes place about 4 to 10 days before an egg is laid. The egg journey down the oviduct is about 3 days. It is during the first day immediately following when the yolk erupts from the ovary and is swallowed up by the infundibulum that most fertilization takes place.