Every UL 924 listed emergency lighting product must provide 90 minutes of emergency operation after AC loss. Here's the code basis and why it's the floor, not a target.
Where the 90 minutes comes from
NFPA 101 Life Safety Code Section 7.9.2.1 requires emergency illumination to operate for a minimum of 90 minutes after a normal-power failure. This number is based on time studies of egress from typical commercial buildings including emergency response delays, people with mobility impairments, and secondary movements (re-entering to help others, gathering at assembly points).
The UL 924 test
UL 924 tests emergency lighting products to operate at their rated output for 90 minutes continuously without an AC source. The battery must deliver its full load for the full 90 minutes. A product that meets the 90-minute floor but fails at minute 100 still passes UL. A product that starts to dim at minute 85 fails.
Why projects sometimes want more
Some occupancies — high-rise residential, certain healthcare, specific hazardous operations — require 120 minutes or more. Check the local AHJ requirements. Sage central battery systems can be sized with larger battery strings to meet extended runtimes; request a runtime calculation with your submittal if >90 min is required.