I see all the examples use a TRANSMITPERIOD = 300. What is the shortest duration this can be set to without affecting reliability?
It's just an example...
A short message takes around 5-15ms to be transmitted, then an ACK takes around that much to get back.
So you can work with those constraints to get your messages across. You can play with the examples and decrease the period.
FWIW increasing bitrate will decrease the transmit times, the default 55.5K will give you the transmit times mentioned above.