Which command entered on a switch configured with Rapid PVST+ listens and learns for a specific time period?

`max-age` defines the maximum amount of time a switch stores BPDU information before discarding it and potentially initiating a topology change, not the duration of the listening and learning phases.

`hello-time` specifies the interval at which the root bridge sends Bridge Protocol Data Units (BPDUs), which is unrelated to the duration a port spends in listening and learning states.

`priority` is a value used in the root bridge election process for a specific VLAN, where a lower priority value increases the likelihood of a switch becoming the root bridge, and does not control state transition timers.

The `spanning-tree vlan 1 forward-time 20` command sets the amount of time a switch port spends in both the listening and learning states before transitioning to the forwarding state. These states are where the switch processes BPDUs to determine the network topology and populates its MAC address table, respectively, without forwarding user traffic.