--heartbeat-period makes more sense as a wall clock time

[nicmcd]

The help says:

--heartbeat-period=PERIOD set time for heartbeats to be published (these are approximate timings, published by the core, to update on progress), default is every 10000 simulated seconds

This functionality would make more sense as a wall clock time sense the resolution of simulated time is very dependent on the type and size of simulation being done. Users would more generally just want to see some information for every N seconds they've been waiting on the simulator. This is a common way to ensure the simulation is actually progressing in time. Some simulators print out the current events/second or cycles/second or sim_time/sec as a metric of simulator performance.

[pdbj]

ns-3 has a similar feature, the heart of which is in the ShowProgress::CheckProgress() function.

(Disclosure: I'm the author of ns3::ShowProgress)