I am not sure what you want from your "motion to strike affiant." It sounds like you want the judge to hit the person who signed the affidavit. If this is the case, it is a feeling that is shared by most lawyers who have been involved in litigation. However, if your intent is to object to what the affiant said in the affidavit, as the previous lawyer indicated, your best move would be to file an affidavit in opposition to the one filed by the affiant. Your question is an indication of the difficulty that many people have when they try to represent themselves in court. You would be well served to engage the services of an experienced foreclosure defense lawyer in your area.
Disclaimer: This answer is provided for informational purposes only, does not constitute legal advice, and does not create an attorney-client relationship. Actual legal advice can only be provided after completing a comprehensive consultation in which all of the relevant facts are discussed and reviewed.
Unless the affidavit has technical deficiencies (for example, not executed in the presence of a notary or not attesting to facts within the affiant's personal knowledge), I believe that you are needing to file an affidavit in opposition attesting to facts different than that stated in the opposing affidavit. If you are intending to file your own affidavit in opposition to a Motion for Summary Judgment, you must file and serve a copy of your affidavit at least 5 business days prior to the hearing, if sent to the opposing party by mail, or if you hand deliver or use overnight delivery to provide it to the opposing party, you must send it so that it is received at least 2 business days prior to the hearing.
It would be the affidavit you would move to strike, not the affiant, although issues regarding the affiant could be a basis to strike the affidavit.
There is no specific amount of time involved.
However, what are you going to use as evidence that the motion should be granted and how are you going to get that before the court in a legally permissible way ?
Please note that the above is not intended as legal advice, it is for educational purposes only. No attorney-client relationship is created or is intended to be created hereby. You should contact a local attorney to discuss and to obtain legal advice.