Ibn Ezra: Hashem was angry at Yisrael in the days of Yavan and Antiyochus, until the Chashmona'im were Metaher the Bayis..

Malbim: It is after the anger will cease.

Rashi: It is the deadline after many days.

Malbim: First he said "l'Es Ketz", and now he said l'Mo'ed Ketz. Es is the natural time, by itself. Mo'ed is a time that someone designated, based on a command or prophecy. First he explained that time obligates all this. They are included in the general order from the days of creation until Tikun ha'Olam. The Ketz will come in its obligated time. Now that the angel informed him, it must come no later than that predicted time due to the Nevu'ah. There is a difference. What is obligated naturally, sometimes Hashem changes it, if man's actions soured. A prophecy for good within a set time cannot be changed. It must come in the time.