Good read on ISS and atmosphere leaks...
https://ntrs.nasa.gov/citations/20110012997
Quote:
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Originally Posted by Trending of Overboard Leakage of ISS Cabin Atmosphere
ISS cabin is maintained at a nominal total pressure between 96.5 kPa (14.0 psia) and 102.7 kPa (14.9 psia) and is composed of oxygen, nitrogen, small amounts of CO2 and other trace gases. The nominal total pressure allows for a livable environment similar to the pressures seen on the ground. The free air volume of the cabin also plays an important role due to the buffer it provides over the range of the nominal pressures. The free air volume is defined as the volume of the ISS that the atmosphere can equalize into. Volume taken up by structure or pressure vessels is not included. The free air volume has increased over the life of ISS due to the additions of modules to the United States On-Orbit Segment (USOS) and Russian On-Orbit Segment (RSOS). The increased ISS volume has extended the response time to having to add nitrogen or air for a given leak rate as well as adding oxygen in support of metabolic needs. At the beginning of 2008 the free air volume of the ISS was 434 m3 (15,318 ft3). After the addition of multiple modules, the ISS free air volume was 899 m3 (31,741 ft3) by March 2011. Visiting vehicles other than Shuttle are included in the volumes numbers. There are nominally 4 visiting vehicles docked to the ISS with the typical complement of vehicles consisting of 2 Soyuz and 2 Progress. An evaluation of a theoretical leak rate of 1 lbm/day air illustrates the benefit of the additional volume to the ISS. At the beginning of 2008, a 0.45 kg/day (1 lbm/day) air would have taken 70 days to drop the ISS total pressure from 102.7 kPa (14.9 psia) to 96.5 kPa (14.0 psia). However by March 2011, a 0.45 kg/day (1 lbm/day) air leak rate would have taken 146 days to drop the ISS total pressure from 102.7 kPa (14.9 psia) to 96.5 kPa (14.0 psia).
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Some take aways for a Mars mission seem to be that the larger the vehicle volume, the more amount of time to resolve a leak; and the more connection ports, the more opportunities for leaks. Since SS has a similar volume to the ISS, it's probably comparable on leakage mitigation timelines. Since it has significantly fewer ports, it should also have significantly less opportunity for leaks to develop in the first place. I imagine a Mars colony (at least an early colony) would likely be built with lots of modules and connection ports, but hopefully with each module being much larger than the modules on ISS.