After your petition is submitted and accepted by the USCIS you will receive a receipt from the USCIS in the mail in approximately 30-45 days.

On the receipt you will see a filing date. This is the date your petition was accepted. In order to determine the approximate time that it will take for the USCIS to process your petition look up the current processing times at:

https://egov.uscis.gov/cris/jsps/ptimes.jsp;jsessionid=abcNqdMAL3x6O-xcA...

At this site simply select the service center where you filed your petition and look for the I-129F.