I agree in part and disagree in part with these answers. Here's why: if you wait 2 months until you're married, then it's considered a related adoption. Under Section 6(D) of the Adoption Act, an investigation is in fact *not required for related adoptions, and neither is an interim hearing (see Section 13). Therefore, you should avoid having to complete background checks, using an agency, and so forth, and you avoid the extra court date for the interim hearing. This saves money and time.
Also, you have additional grounds of unfitness available to you that are strong (see the definition of unfitness for "intent to forego parental rights" in Section 1's (n)(2)(ii), which is only available as unfitness grounds when you, the mother, bring the petition to adopt, and which basically only requires that you've not received financial support from him).
You have a good case on unfitness either way if he's never been involved, and many grounds would apply. Please note that you still are required to identify the bio father's identity in an affidavit, and therefore he'd be required to receive some sort of notice under Section 7(C) of the Act. If you don't know where he is, that means in your affidavit you state his last known whereabouts; if you cannot locate him, then you can publish and default him on his rights. You should consult an attorney especially regarding the specific grounds of unfitness that apply and how much of a search you are required to conduct for the bio father before being able to default him.
Once his rights are terminated, you should be able to finalize either on the same day or soon after, depending on local practice of the Freeport courts.