Delayed implantation is a delay in the development of the embryo. The cluster of cells (blastocyst) does not immediately attach to mum in the womb (implant in the uterus). This adaptation is used by some mammals to delay the birth of the baby until there are better conditions for it to be born.
Lifecycle is the series of changes in the life of an animal from birth to adult.
Lifespan is the length of time an animal usually lives.