The Gemara in Rosh Hashanah 11a tells us that in Nissan we were redeemed and in Nissan we will be redeemed; may it be His will, amen. The Gemara in Nazir (43) says that if one says that he will become a nazir on the day that Ben Dovid comes he is prohibited from drinking wine from then on; i.e. he becomes a nazir immediately. The Shaagas Aryeh (Turei Even Rosh Hashanah 11b) asks, why does one become a nazir instantly? He should only become a nazir in Nissan since that is when the geulah will come.
The Sha’agas Aryeh points out that the answer is based on a Gemara in Sanhedrin 98a that poses a contradiction in a pasuk in Yeshayah (60:22). The pasuk says in reference to the geulah, that it will come “b’ieta –in its time,” and then, in the same pasuk it says, “achishena – I will hasten it.” The Gemara resolves the contradiction by saying that if we are zocheh, Hashem will hasten the geulah; if we are not zocheh, it will come in its time.
The Shaagas Aryeh explains that when the Gemara says that we will be redeemed in Nissan it is referring to the set time for the geulah, which is in Nissan. However, Mashiach can actually come in any month of the year.
This is also the understanding of the famous Ani Ma’amim in which we state that we believe that Mashiach can come any day. How can we say that we are waiting for Mashiach in any month other than Nissan? The answer is that while Nissan is the designated time for the geulah, it can still come on any day.
What is the difference between Mashiach coming at the designated time and his arrival on any other day? Perhaps the difference is how difficult it will be for us to be zocheh to the geulah. We know that one of the middos that Hashem runs the world with is makdim refuah l’makkah – He creates the cure before the blow. Rav Naftali Trop zt”l explains that Hashem acts with this middah in order for the yeshuah not to “cost” us so many zechuyos. If we were in a predicament that required Hashem to create a refuah, it would require many zechuyos. Since the remedy is already in existence it is easier for us to attain it. Hashem creates the refuah before sending the makkah, thereby lowering the amount of zechuyos necessary to bring the preexisting refuah.
Similarly, when it is the zman that is destined for the geulah, fewer zechuyos are required to bring it about.
On a similar note, I recall that, toward the end of Rav Shmuel Berenbaum’s life when he was in a very weakened state, we had asked him if he would give a chaburah in the afternoon in addition to the hour-and-a-half long shiur he gave every day. He responded that he “didn’t want to be matriach (bother) the Eibishter too much.”
We see from the Gemara that Hashem built in to the briyah that Nissan is a time for geulah. Therefore, it is not “asking for too much” from Hashem when we daven for the geulah in Nissan.
The Gemara in Sanhedrin ibid compares the coming of Mashiach to childbirth, where there are occasionally stillbirths. There have been many “b’ietos,” i.e. “due dates,” that have produced stillbirths in the past. As we enter the next “due date” of the month of Nissan, may we be zocheh to the birth of a new era; that of the coming of Mashiach tzidkeinu, b’meheirah b’yameinu, amen.