After in-vitro fertilization, the embryo can be transferred after 3 days or after 5 days.

Here are advantages and disadvantages:

Day 3 Transfer (4-8 cell stage)
Best when there are less than 6 embryos, poor embryo quality, or prior IVF failures. 

• Advantage: Embry returned early to natural environment and additional embryos freeze well
• Disadvantage: May be difficult to choose the best embryo and may freeze nonviable embryos

Day 5 Transfer (Blastocyst, 60-100 cells)
Best when there are many good quality embryos

• Advantage: Selection of best quality embyos and decreases chance of multiple pregnancies
• Disadvantage: Embryos longer in laboratory and blastocysts don't survive freezing well