Verb Tenses and Auxiliary Verbs

Our train leaves at four-thirty tomorrow morning.

This is probably a simple problem, but I am having difficultly finding a source that answers my specific question. I am having some trouble determining the tense of leaves here, and determining tenses in general. The sources (here's one example, but I am referring to basic guides) I have read imply that a lack of any auxiliary verbs (beyond will for future simple) automatically indicate simple tense. Is this true? For example, leaves is present tense on its own. However, in the context of this sentence, the train is clearly departing at a specific time in the future.

How do I determine the tense? Is it present simple because there are no auxiliary verbs, and leaves on its own is present, or is it future perfect because it "describes an action that will be completed by a specific time in the future." Is it neither?

Does the context of a sentence change the tense of a verb like this? Or am I entirely off the mark in how I'm determining tense? Grammar resources like the one I linked are useful, but I am still finding myself lost. Any links to more exhaustive and nuanced explanations/resources would also be appreciated.