Hi

Quick question

Can imperial unit perform free attack action using standby token given by "Deploy the garrison" and then in its activation perform normal attack action?

My understanding is that one can use only single attack action per activation, but attacking using free standby token takes place outside of activation window. Am I correct?

You are correct.

Yes, just remember that the standby attack has to take place before the unit activates, or it will lose the standby when it performs any action during its activation.

Also, you can only perform 1 attack action PER ACTIVATION, not per round. It is a key distinction which allows Palp to let units attack twice with Pulling the Strings. In theory if a unit has standby from DtG, and Palp is in play. They could get 3 attack actions in the same round. (standby, their activation then Palp's activation.)