How can I check the time response of my model in Gazebo?

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Hi, Gazebo publishes the pose and the twist of every link on /gazebo/link_states topic.
You should be able to plot the velocity of a given link using this message.

To know the index of the link you want to monitor you can check its index in the list /gazebo/link_states/name
Then you can plot /gazebo/link_states/twist[INDEX_YOU_FOUND].

I don't know how often this message is published but it should allow you to monitor your twist and thus know how long it takes to reach the desired velocity.

Hope this helps,