Why do two apps show different elapsed time for the same hike?

The short answer

If you are looking at one recorded file that got opened by two different apps or services, the elapsed time will always match — it is baked into the file as two timestamps, and reading a timestamp is not something two apps can disagree about. The gap shows up in a different, much more ordinary situation: you started two separate recordings of one walk, one on each app, because you were comparing them or handing a phone to a hiking partner. Each app only knows about its own start and its own stop, and those two moments were never going to land on the same second.

Two very different meanings of "the same hike"

It matters which of these actually happened, because they behave completely differently.

One recording, opened twice

Export a hike as a GPX file and open it in two separate services, and both are reading the identical start and end timestamps out of the identical file. There is nothing left for them to disagree about — elapsed time here is not computed so much as copied.

Two recordings of one walk

Run two apps at the same time, on the same walk, and there is no shared file at all. Each app produced its own track, with its own first point and its own last point, from its own start button and its own stop button. Two independent recordings of the same real event are not the same recording, even though the walk itself was identical.

Why the start rarely lands on the same instant

Tapping "start" on two phones, or two apps on one phone, one right after the other, is not a simultaneous action even when it feels like one — a second or two of lag between the taps is ordinary and usually harmless on its own. The bigger gap tends to come from what happens after the tap. Recording a route depends on the phone having found enough satellites to fix a position, and that search does not take exactly the same amount of time twice, let alone across two different apps or two different phones with two different views of the sky at that moment. One app beginning to log points ten or twenty seconds before the other, even though both buttons were pressed together, is enough on its own to put daylight between two elapsed-time totals.

Why the stop rarely lands on the same instant either

The end of a hike has the same problem in reverse, and it is usually the bigger contributor of the two. Reaching the trailhead, you stop the first app, and only then reach for the second phone, check the screen, and tap stop on that one too — a gap of anywhere from a few seconds to a minute or more, depending on how much you were juggling at that moment. Nothing about this is a malfunction in either app. It is just two people, or one person operating two phones, doing one thing and then the other rather than both at once.

The gap is a fixed offset, not a growing error

A useful thing to notice is that this kind of gap does not scale with the length of the hike. A thirty-second lag at the start and a forty-second lag at the end adds up to roughly the same minute and change whether the walk lasted forty minutes or four hours. That is a good way to tell this cause apart from something wrong with the recording itself: a mismatch that stays roughly constant in size points at start and stop timing, while a mismatch that grows across a long hike points somewhere else entirely.

The one situation this does not explain

If there was only ever one recording — a single GPX file, exported once and opened in two places — and the elapsed time still comes out different, none of the above applies, because there was no second start button and no second stop button involved. That points at something else: a timezone handled inconsistently by one of the two services, or the file having been edited between the two viewings. Worth ruling in the right cause before assuming it is the same start-and-stop-timing story as two live recordings.

Where TrailCam fits in

TrailCam waits until it has found enough satellites before a recording begins, which is exactly the kind of delay that can put two side-by-side recordings a little out of step with each other at the start. Once running, the route keeps recording in the background whether the screen is off or you have switched to another app, and duration is reported as moving time, with any time you paused by hand kept out of it. The app is free to download.