It varies, depending on the volume of applications. This from the UKBA info page:
Nationality contact centre
Our staff are unable to check the progress of your application and cannot provide any information about your application if you applied less than 6 months ago.
We strongly recommend that you check with your network provider for potential costs before calling. Phone calls may be recorded for quality purposes. Our current average customer waiting time is approximately 3 minutes. Your wait may be longer if you call at the beginning of the week.
Phone: 0845 010 5200
Email: ukbanationalityenquiries@ukba.gsi.gov.uk
Assuming (from your previous post and her timeline) that your girlfriend is applying as the wife of a British Citizen, the application would only be void if the divorce decree absolute had been granted.