I recorded an hour of the local NOAA weather. It took 56MB of space on the microSD card. This was continuous audio, which you won't have on many systems (some of the top 50 streamers I'm sure run above 50% during their busiest times) . The HP1 eliminates all the dead air in between transmissions, so normally you'll see much less than 56MB required per hour.
My card had about 60 MB used (HPDB plus favorites and standard files). With the available space, I could have recorded 34+ hours of continuous audio and a much, much more from a typical system, as Jay indicated.