If upon attempting to upload a GPS file you see an error message telling you that "Time information is missing from file," this means that unfortunately your file is incompatible for upload to Strava.
The problem is that your file likely contains only GPS data and no timestamp associated with each latitude and longitude coordinate. Opening your file in a text editor might reveal something like this:
<trkpt lat="37.7808230" lon="-122.3956800">
Without timestamps, it's impossible for Strava to calculate your speed and time on segments, so the files will be rejected upon upload.
There are a few common sources for files like this.
If you are a Strava Premium member, you have the ability to download the .GPX files from other users' activities. However, these files will not contain time information. If you are trying to 'copy' an activity from another Strava user with whom you ran or rode, you can do so by asking them to export and send you their own .GPX file; when they do so that file will contain timestamps.
Another common source for these files is .GPX files exported directly from MapMyFitness sites. These files do not contain workout data, which includes timestamps. However, you can try this third-party workaround, a tool that is available on the web (but is not affiliated with Strava or MapMyFitness):
It will extract your data from MapMyRide as a TCX file which will include your GPS, time, and accessory data like Heart Rate and Cadence.
Thanks very much!
Strava Support Team