So you only have 1 spare wire, in which case you can't use 485 for another signal to help with the protocol.
Of course if you have a main module you don't need this timing signal, just get the master to ask for data every second. In which case you then have two spare wires and can use 485 on them to help with the protocol, maybe along the lines of what I said above.
Technically it's not necessary but such a signal can reduce the load on slave processors.
Rob