I get this question quite a bit because people are confused on how the tool works. The incorrect way to change the start time of an activity is to try and use the TRIM feature (unless you're actually trying to trim off part of your activity). The screenshot below indicates the TRIM feature:
- This is not the correct way to shift the start / stop time of an activity. It only works to trim (or "crop") an activity. In other words, you need to be making either end of the activity shorter.
What these people want to do is to "Time-Shift" an activity. When you do a "Time Shift", you are effectively, moving the start and stop time of your activity entirely. You're not trimming (cropping) off the beginning or the end; you're moving the time stamps for the entire activity... shifting them... to a new time.
Here are the steps:
1) Upload your activity to the timestamp tool:
https://gotoes.org/strava/Add_Timestamps_To_GPX.php
2) Select your Correct Time Zone (or select for the tool to “Let Tool Guess My Time Zone”.
3) Check the box that says, “Time Shift”.
4) Enter the Activity Start Time that you desire. Leave everything else blank.
5) Click the Upload button.
6) There should be no need to use the TRIM feature on the next page.
- Correct way to change the start time and stop time of an activity. Note the check box for Time Shift.