Is it permissible for a pilgrim to cast the three Jamarāt (stones) on the days of Tashreeq (the eleventh, twelfth, and thirteenth) on the night of the twelfth, after midnight, and then immediately depart Makkah?

If you left the stay overnight in Mina during the Tashreeq nights due to an excuse, then there is nothing upon you. But if it was due to negligence, then a دم (sacrifice) is required of you. Combining the throwing of two days [of pebbles] into one day is permissible. And if you threw all the pebbles of the Jamarat on the third day of Tashreeq, your throwing would be valid as an अदा' (performance). Throwing on the third day before Zawal (midday) is a matter of dispute: the majority of jurists do not permit it, while some have permitted it, such as the Hanafis and one narration from Ahmad. If you did so in imitation of those who permitted it, then nothing is binding upon you. But if it was not in imitation, then it is invalid and a دم (sacrifice) is required of you.