It's not an imperative "tense" per se. It's more of an imperative mood/mode or context. While the attached Grammarly link discusses this, based on the definition of imperative, an easy way to think of it is that imperative statements create a relationship/context between the speaker and the listener where a response is expected. The imperative statement is a request to act or expression of expectation for action or result, e.g., such as a response to the statement. That statement is imperative as it is important for or related to what is to follow. It creates a situation or context of expectation from the participants. The imperative statement sets the stage for what's next.
Example: "Please remember to pick me up from the airport at 9:00 AM."
Note, the stage is set for a response, action, agreement, etc., to follow. The statement is needed, important, related to what follows.
https://www.grammarly.com/blog/imperative-sentences/