On average? Well, the Fluther admins could run a tool to determine the exact value. It’s all in the web log files.
Web log analysis software (also called a web log analyzer) is a simple kind of Web analytics software that parses a log file from a web server, and based on the values contained in the log file, derives indicators about who, when, and how a web server is visited. Usually reports are generated from the log files immediately, but the log files can alternatively be parsed to a database and reports generated on demand.
http://en.wikipedia.org/wiki/Web_log_analysis_software
There’s lots of free open source stuff.
My estimate for an average? About 20 seconds.