Thank you for that, I know i need to look at this a lot more but this does confirm that these are half duplex devices. So its send data then listen then send then listen. If you want to create a multi node network its more like created a bus type network topology.
and i think your idea of polling would work fine.
Each remote device could be sensing events and storing an event ID + milies since last poll that event happened. Then when its polled it just needs to send these two values, the master device if has the time stamp of the "last poll" it can calculate the events realtime time stamp using the milies as an off set.
The actually Idea is to have a race track with (lets image) 4 checkpoints. Each of these check points can sense the cars as they pass through and identify each one. This sensing will be done by an ardunio board, Probable an IR LED on the bottom of the car passing over a photo sensor. and i was thinking each car will flash its LED at a different rate and to could the number of pluses over a time frame to see what car is going past.
So then once it has the car ID and the time stamp it will transmit this back to a raspberry pi. the Pi will work out split times, speeds, etc etc, and then send back to the ardunio a array value that it will use to light a RGB Led strip / array on the check point. showing what order the cars passed though the checkpoint, who was fastest between the gates, who hasa made up places /lost places etc etc.
So each gate will sense the cars and control the LED displays. but the CPU grunt work will be carried out by the Pi, which will me I am not limited by the memory on the Ardunio boards and I can also combine the data from all the Checkpoints before deciding what each LED display should show.
As long as I can do a poll all the check points at about 5-10Hz this would be fine, so each poll from the pi would be
- have you any news for me
- set your LED display to this .....
each of these are very small payloads and don't need to be real time. updating the gate 5 times a second is plenty fast enough even once a second would be OK, its really once all the cars have been though to change to show spectators what happened (some thing that can be hard when watching RC racing cars across the other side of a room / field)
Cheers for the info very useful to get an idea of what can be done 
Robin2:
You need to describe what you want in a lot more detail.
Normally an nRF24 talks to one other nRF24 which acknowledges the message. You can arrange for several "slaves" to listen on the same address but then you have to disable the acknowledgement process.
Using the one-to-one system you can create a hub-spoke system because each message takes very little time.
This Simple nRF24L01+ Tutorial may help.
If you can arrange for one nRF24 to act as master and poll the others in turn using the technique in my second example that will probably be the simplest system. However I recognize that it is not suitable for every situation - hence the need for more detail from you.
My link includes a link to TMRh20's RF24 library. There are other variants that add Network and a Mesh features on top of the basic library - but I have not needed to use them.
...R