I think we have a little translation error around "lecture". "Lectura" in Spanish could be translated as "reading" so maybe that would be a better word to use?
Your system only even looks at the GPS when the value is high. That's wrong. The GPS data is always coming in the serial port. You should always handle it. Otherwise the buffer can fill up and new data is discarded - the buffer is full of old data from just after the value went low.
When you get a valid GPS sentence, you need to know the time that ocurred, with millis(). The GPS library may do that for you. Then when you get a high-to-low transition, take the last GPS time and add the elapsed time. The last GPS fix may have been 10 minutes ago and you will still get a very accurate time reading.