# The Most Expensive Milliseconds Are Unmeasured

DevFeed: [The Most Expensive Milliseconds Are Unmeasured](<https://devfeed.tech/articles/the-most-expensive-milliseconds-are-unmeasured-19739.md>)

Original publisher: [Read original article](<https://medium.com/expedia-group-tech/the-most-expensive-milliseconds-are-unmeasured-d6cfaaca881d?source=rss----38998a53046f---4>)

Author: Divya Gupta Arora

Published: 2026-06-03T17:11:58Z

Content type: article

Language: en

Sources: [Expedia](<https://devfeed.tech/sources/expedia.md>)

Topics: [Mobile](<https://devfeed.tech/topics/mobile.md>), [render](<https://devfeed.tech/topics/render.md>), [ui](<https://devfeed.tech/topics/ui.md>)

Tags: [case-study](<https://devfeed.tech/tags/case-study.md>), [devops](<https://devfeed.tech/tags/devops.md>), [engineering](<https://devfeed.tech/tags/engineering.md>), [login](<https://devfeed.tech/tags/login.md>), [mobile](<https://devfeed.tech/tags/mobile.md>), [mobile-apps](<https://devfeed.tech/tags/mobile-apps.md>), [mobile-performance](<https://devfeed.tech/tags/mobile-performance.md>), [observability](<https://devfeed.tech/tags/observability.md>), [performance](<https://devfeed.tech/tags/performance.md>), [release](<https://devfeed.tech/tags/release.md>), [software-engineering](<https://devfeed.tech/tags/software-engineering.md>), [technology-investments](<https://devfeed.tech/tags/technology-investments.md>), [time-to-interactive](<https://devfeed.tech/tags/time-to-interactive.md>), [ui](<https://devfeed.tech/tags/ui.md>), [visibility](<https://devfeed.tech/tags/visibility.md>)

## AI overview

This Expedia Group engineering case study describes extending Native Time to Interactive across mobile login screens. The metric was used to evaluate technology investments, compare platform behavior, and detect performance regressions that existing system-health signals did not reveal.

## Source excerpt

Expedia Group Technology -- EngineeringHow a screen-level performance metric reshaped platform decisions, engineering ownership, and release disciplinePhoto by Pietro De Grandi on Unsplash For the last few years, my responsibility has been straightforward to state but hard to execute -- owning the traveler login experience across mobile platforms. Not just whether a feature works, but whether it feels responsive, predictable, and trustworthy in the moments that matter most. During login, those moments are unforgiving: if a login screen hesitates travelers don't interpret it as 'a slow render', they interpret it as risk. And when the majority of travelers interact through our mobile apps, performance stops being a technical concern and becomes a product promise. This post is a case study of how, within Expedia Group™'s login domain, we extended Native Time to Interactive (NTTI) across login screens -- moving performance from a late-stage check to a first-class signal we can use to validate technology investments, compare platform behavior, and prevent silent regressions as we ship. The Problem: Mobile reliability rarely fails loudly Mobile performance rarely breaks with a crash. It usually degrades quietly, a button takes a beat longer to respond a screen looks ready, but taps don't register the UI stutters just enough to feel "off" Those are the expensive milliseconds -- because they erode trust without triggering obvious alarms. In our login flows, we were shipping consistently, evolving a major part of our stack, and supporting increasing product complexity. Yet we didn't have a consistent way to answer the user's real question -- "When can I actually use this screen?" Why our existing signals failed We were not blind. We tracked many useful things, crashes and ANRs backend latency and service SLIs some component-level timing signals limited Time to Interactive tracking on onboarding and initial login But we had a gap -- we had visibility into system health, not screen