I'm married to an Italian citizen, and next week we will be going to the Italian Consulate with jurisdiction in the place in which the marriage took place as we want to our marriage to be registered in Italy; my question is how long it will take our marriage to be transcribed in Italy?
The answer is: Depends.
After the Italian Consulate accept your instance for the transcription (assuming you have all the required documents and translations) the Consulate will transmit all the documentation to the Italian City (Comune) where your partner has the residence.
Based on the size and the workload of the office in that specific City, the time requested for the transcription can take from days to weeks.
Normally after submitting the instance your partner should contact the City's office in order to check if they got the documentation in the first place.