Is the throwing valid if it was done on the eleventh and twelfth days by combining the throwing of both days with a single intention for every seven pebbles for each Jamrah, and what is obligatory for someone who did that?

The pilgrim stones the three Jamarat: the Minor, then the Middle, then the Major, with seven pebbles for each Jamarah on the Days of Tashreeq. It is permissible for shepherds, the sick, and those for whom repeated daily trips are difficult to combine the stoning of two days or more. When combining the stoning, it must be done in order of the days: so, one stones all the Jamarat for the first day, then all for the second day, and so on. It is not permissible to stone one Jamarah for several days all at once. If someone misses stoning for an entire day, a sacrifice (dam) is obligatory upon him if he is wealthy; otherwise, nothing is due from him.