LapTimer does not work with the internal GPS on a Nexus 5. On launch, it shows no fix and the following status:

Overall status: Not Ready (red)
LGE Nexus 5 GPS (green)
GPS Position (red)
Accuracy (red)
Storage 0.0 GB (green)
Calibration (red)
Track nearby (red)

The GPS page stays at "Acquiring ...