Sorry small mistake. I was thinking about 1 Hz PGN129029/GNSS, but there is also 10 Hz PGN129025/LatLonRapid. But not all GPS provide PGN129025. And specially if you have old NMEA0183 GPS with converter, there is only 1 Hz PGN129029.
And if you are planning to put other GPS to the bus by yourself, then you can provide PGN129025 with 10 Hz and PGN129029 1 Hz to the bus.
PGN129025 is single frame higher priority message. One frame transfer takes about 400 us. Since bus is multimaster bus, there may be others sending data at same time and our frame transfer may be delayed. Lower source address has higher priority. So you can try to set your device source address to 0, but then depending of other devices on the bus higher priority devices may rise your source address during address claiming procedure. But in normal boat bus I would expect that extra delay would be very rare.
So if you sending lat/lon in 100 ms period, the transfer delay should be less than 1 ms, which is <1/100