Should the Maghrib and Isha prayers at Muzdalifah be delayed until the time of Jam' al-Ta'khir, or is it permissible to offer them earlier?

The correct view is that when a pilgrim reaches Muzdalifah, he should pray Maghrib immediately. If he arrives before the time for 'Isha' begins, he should pray Maghrib and then combine 'Isha' with it as a "collection of advancement" (jam' taqdim), to facilitate matters for him and to preserve his ablution. This is what is practiced in our current time. It is known that Ibn Mas'ud (may Allah be pleased with him) would pray Maghrib and then wait for 'Isha' to pray it at its appointed time. This indicates that he believed 'Isha' should not be combined with Maghrib if one reached Muzdalifah at Maghrib time.