duvin Immigration would only grant one 96 hour free transit visa per reservation (per person) and this excluded STPC, which use the new visa type, twice in a reservation. However since the advent of visa free access and the +Qatar offer things may have changed. In fact I speculated that due to those two measures STPC was no longer required for transits of 12 hours or more and could be stopped except for 8-12 hour transits. Whilst it has been possible to find the webpage it is not linked into the current version of the QR website and you need to know the exact address to reach it.
As I say that was speculation some months ago and things may have changed since then.