When will the redemption be Achishena? At it's appointed time.

Mitteler Rebbe, Maamar Al Tatzer Es Moav (free translation)

It must be understood that truthfully the statement of the sages אם לא זכו אחישנה "if they [Yisroel] do not merit, [then the redemption will be specifically] b'itah [in it's time]" refers to the specific time of the elevation of Knesses Yisroel Above, which is dependent on an eis ratzon (desired time) and the desire of the Bestower, davka. But this itself is "achishena" ("I will hasten it") which is according to the simple meaning of the verse that davka "b'itah, achishena" ("in it's appointed time [is when] I will hasten it"), not [as is commonly thought] that it is divided into two opposite things of "if they merit I will hasten, and if they do not merit it will come in its appointed time", as if to say that "achishena" is not "b'itah".

The truth of the matter is that even though it seems like two opposites: that at the appointed time [Hashem] will hurry it and bring the redemption before its time, actually it is not like that. The truth of the matter is that specifically at its appointed time, which is the time when the level of Malchus which is Knesses Yisroel is elevated and recalled for good[...]then specifically at this time the end will be speeded up.