Gigazelle, you are right: hourly data works for non-conversion variables, but doesn't for conversion. I just found a workaround on how to get hourly data for covnersion variables as well, I first select the time period for a non-conversion report and then switch in the "extract data" page to another covnersion report. It remembers the settings and I can request hourly data for conversion report as well.
In step 1 of the data extract click on the date which should open the choose date window. Then at the bottom of the screen under selected granularity in the show by drop down choose hourly. See the screen shot below.