We discussed something similar last week - here are the strengths - and it explains why some last longer than others given the concentration of perfume.
Eau de Perfume (or Eau de Parfum)
As its name suggests, Eau de Perfume is a diluted version of Perfume, usually containing between 8% and 15% perfume oil. Since it has less perfume oil, it's also less expensive, but still provides a fragrant scent for up to 5 hours. This makes it a good alternative if you want the longer lasting effect of a Perfume without the hefty price tag.
Eau de Toilette (EDT)
Eau de Toilette is a lighter version of Eau de Perfume that is considered a ‘middle of the road' fragrance as it is less expensive and only lasts up to 4 hours. Containing between 4% and 10% perfume oil, Eau de Toilette is popular among men, who prefer to have a fragrance that doesn't overwhelm the senses or last all day long.
Eau de Cologne (Cologne)
Eau de Cologne is often confused with Eau de Toilette as they both provide a light smelling fragrance. However, Eau de Cologne has less perfume oil, usually containing between 2% and 5%. This makes it more affordable and shorter lasting than Eau de Toilette, so it's commonly used by men who want a splash of fragrance to start their day or night.
Aftershave (A/S)
Aftershave is often believed to be stronger than Eau de Toilette or Eau de Cologne. This is probably because they have the word ‘eau' (French for ‘water') in their name, which could be taken to imply that they are watered down. However, Aftershave contains only 1% to 3% perfume oil. It isn't meant to last too long because its main purpose is cooling and soothing the skin after shaving, which is where its name comes from.
Personally I find these timings to be on the low side as a decent EdT certainly stays with me for longer than 4 hours.