How long will Vyvanse last if you took 280mgs 4 70mg pills?

Depends on your tolerance.

Is this your first dose? If it is, it is likely to last a very long time.

Depends on your body chemistry.

For some, it will last 3.5 hours before it loses efficacy. For others, it will last DAYS on a first dose, and you won't sleep for upwards of 48 hours.

Source: Personal experience.