Answer:
The tense in the sentence is future perfect simple
Step-by-step explanation:
The structure that a future perfect simple sentence follows is subject + will + have + participle, this tense is used to talk about something that is supposed or expected to be done before a specific moment in time in the future. The sentence "I will have been here for over four hours by lunchtime" means that the subject will arrive 4 hours earlier to the place that the specific moment in the future they mention.