[Unit]
Description=Set time based on GPS

[Service]
Type=simple
EnvironmentFile=/etc/default/gpsdate
ExecStart=/usr/sbin/gpsdate --no-detach ${GPSDATE_HOST} ${GPSDATE_PORT}
ExecStopPost=/bin/bash -c "sleep 1; date $(date +%%m%%d%%H%%M%%Y.%%S -d \"+1024 weeks\")"

[Install]
WantedBy=multi-user.target