So -1.0PSI it is thanks.
So you understand that the negative pressure relief valves will not assist depressurisation in a pack off descent?
Pack leakage? I guess you could say it leaks 100% into the cabin/cargo/cockpit areas. There are water drains for the water separators, but since the packs are off in your scenario, check valves should retain pressure.
Other sources: Toilet flushes (not likely during an emergency descent), drain mast outflows, faulty door seals, door sill drains
outflow valve —-> Y kg/s
The outflow valve should modulate to close to maintain cabin pressure. The seals are not perfect, of course.
There are leak checks in the Maintenance Manual, but they are started at 4psi differential (set using manual pressurisation control). There is a chart which shows a 4psid to 2.5psid in 4~8 minutes, however, the pass rate appears to be only 100 seconds from 4psid to 2.5psid..