Does crossing a time zone mid-hike affect your recorded time?

The short answer

No. Crossing a time zone during a hike, a ride, or any other recorded route has no effect on the distance, duration, moving time or pace shown afterwards. Every point in a GPS recording carries an absolute timestamp — Coordinated Universal Time, the same reference regardless of where on the planet you happen to be standing — and every duration figure is built by comparing those absolute timestamps to each other, not by reading whatever hour the phone happens to be displaying at that moment. The local clock can change mid-walk. The arithmetic built on top of it does not.

Why the underlying clock never actually moves

A GPS recording does not store "twenty past nine in the morning" against a point. It stores a single instant expressed in UTC, the same convention a GPX file uses in every timestamp it writes for exactly this reason: a route recorded on one continent has to mean the same thing when it is opened on another, and the only way to guarantee that is to measure everything against a reference that never changes no matter which zone you are standing in. Duration, moving time and pace are all computed from the gaps between these UTC instants — the last point's timestamp minus the first, or the sum of the gaps between consecutive moving points. None of that arithmetic has a "which zone am I in" step anywhere in it.

What actually changes when your phone crosses the line

An iPhone set to update its time zone automatically will relabel the hour the moment it detects the crossing, and the clock on the lock screen can jump forward or back as a result. What moves is the label attached to a given instant — the word used to describe it out loud — not the instant itself. The point recorded one second before the crossing and the point recorded one second after it are still exactly one second apart in UTC, whatever the two clock faces either side of that second happen to read.

This is really the same distinction that shows up whenever a GPX file looks like it started at the wrong hour after being uploaded somewhere: the coordinates and the underlying timing are untouched, and only the human-readable clock time layered on top is what moved.

Why this would break a stopwatch, but not a GPS track

A method that genuinely would break here is writing down the wall-clock time you started, writing down the wall-clock time you finished, and subtracting one from the other by hand. Cross a time zone in between and that subtraction is simply wrong — you are subtracting two numbers that were never on the same scale to start with, the same way subtracting a temperature in Celsius from one in Fahrenheit gives a meaningless answer. A recorded track never does this, because it was never subtracting two local clock readings in the first place. It was always comparing two absolute instants, and an absolute instant does not care what a nearby clock face happens to be displaying.

A daylight-saving change works the same way

A hike that happens to straddle a daylight-saving clock change is really the same situation on a smaller scale — the local offset shifts by an hour without a physical line to cross. It carries no special risk to a recorded duration for the same reason a time zone does not: the offset is a label applied to an instant for display purposes, and the instant it is being applied to is unaffected either way.

Things that trip people up

• Seeing a start time and an end time that look inconsistent with each other on a route that crossed a zone, and assuming the duration must therefore be wrong — the displayed times can look odd while the actual duration between them stays correct, because that duration was never derived from the two printed labels.
• Manually adding up a multi-day trip by subtracting the local start and end times you jotted down somewhere — this is exactly the case that does break, and it has nothing to do with how a GPS recording itself handles the same crossing.
• Assuming a phone needs to be told which zone it is in for tracking to stay accurate — it does not; the recording keeps writing absolute timestamps the entire time regardless of what the phone believes the local zone to be.
• Worrying that a route paused right at the moment of crossing will behave differently — it will not. A paused stretch logs no points either way, so there is nothing for a zone change during a pause to touch.

Where TrailCam fits in

TrailCam records a route in the background the entire time you are out, reporting distance, moving time, pace and elevation gain from the points it actually logs, and exports the result as a GPX 1.1 file using the same UTC convention every conformant GPX file relies on. None of that depends on which time zone the phone believes itself to be in at any given moment, on a multi-day tour or a single afternoon alike. TrailCam is free to download; GPX and CSV export are part of the optional TrailCam Pro upgrade.