Translation:I will have missed the bus after lunch.
I will have missed the after lunch bus?
After lunch, I will have missed the bus
What does the Portuguese mean?
The after lunch bus would be the one that leaves (just) after lunch, as opposed to the before tea bus, which leaves later (just) before tea(time).
[JOKE ON] Good grief Luís, don't you know anything about sacred rituals?? [JOKE OFF]
The future perfect tense indicates that something will happen by some point in the future. There is certainty about this. This tense is almost always used in more complex sentences - different from DL's unhelpful example.
By this time next year, Trump will have been president for three years.