The time taken for the K1 fiance visa process varies with each individual case. However, in general, a fiance visa application may be slightly quicker than an application for an immigrant visa, as immigrant visa petitions are taking longer to be processed and approved by the USCIS in the U.S. If the time factor is of importance, you should contact the USCIS office where you will file the petition to ascertain processing times before deciding on applying for a fiance or immigrant visa.
You are required to file a petition with the USCIS to have the conditional resident status removed. The petition must be filed 90 days before the second anniversary of your spouse being admitted into the U.S on an immigrant visa, or adjusting status on marriage, if your spouse entered on a fiance visa.
No, if the marriage will not take place within 90 days your fiance's arrival in the U.S., it will not be possible to process an application for a fiance visa. If your intent is to eventually marry in the U.S. Visa free travel under the Visa Waiver Program or a nonimmigrant visitor or work visa is not appropriate.