The FISC has its own website which happens to answer your question right on the "About" page[1]:
The Court sits in Washington D.C., and is composed of eleven federal district court judges who are designated by the Chief Justice of the United States. Each judge serves for a maximum of seven years and their terms are staggered to ensure continuity on the Court. By statute, the judges must be drawn from at least seven of the United States judicial circuits, and three of the judges must reside within 20 miles of the District of Columbia. Judges typically sit for one week at a time, on a rotating basis.
> ...and that article suggests that (if we accept they rotate duty and meet monthly say) they spend, on average, (8 hours / 133 * 60 minutes) ~3.5 minutes carefully evaluating each application. If not, it's ~30 seconds per application.
No, the article says 33 per week. The judges aren't meeting together every few months; the sitting judge is replaced by the next every week or so. Assuming an 8 hour work day and 33 warrants per week, that (8 * 5) / 33 = 1.2 hours per warrant on average.
[1] http://www.fisc.uscourts.gov/about-foreign-intelligence-surv...