Puzzle n°29 (*) - The hourglasses

One day, a nice somali girl called Samiole was once captured by the awful Raminagrobis...
who however accepted to free her, but under one condition !

Raminagrobis gave Samiole one hourglass lasting 7 minutes and another lasting 4 minutes,
and asked her to measure exactly 9 minutes starting at a moment Raminagrobis himself would choose.

Poor little Samiole was worried, but having exercised her neurons,
she thought there must be a way out !

Will you find a solution ? If you were Samiole, would Raminagrobis have freed you, or eaten you ?

... I'm giving up ...