Nodes in the NetSim retrieve time from the same (single) virtual clock that ticks virtual time within NetSim. As such, they can be considered perfectly time-synchronized. Real-world clocks drift from a reference clock due to various reasons (heat, deficient oscillator, etc.,), resulting in an offset of a few milliseconds per day.
In NetSim, clock drift is not available. This means that it is not possible to model clocks to run with different rates and/or offsets, in different nodes/sensors.