How many simultaneous Modbus TCP masters are supported?
Is there a delay when answering two masters with the same request?
Yes, multiple masters are supported in Modbus TCP. There is no set limit to the number of masters, but the slaves can only answer one master at a time. Technically there will be a delay if both try to poll the slave at the same time as one of the masters may have to resend the command. You will probably have to use trial and error to come up with the best poll rate in this case.
There is a limit on simultaneous connections though, which is 10.