I don't think you can do this with Axon, you'd probably have to do it at the client (voip phone) end.
For example you can have a program force Express Talk to disconnect a call using
"C:\Program Files\NCH Swift Sound\Express Talk\talk.exe" -hangup
For IVM, you could have an external program set a variable in IVM after the time limit that would indicate the call should disconnect. Then on the start of an OGM you can check if the call should end based on the variable.