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A. I will make the adjustments on the report. (simple future)

B. I will be making the adjustments on the report. (future progressive)

Is there a difference in meaning between the sentences above?
Or is there an implied time for the verb between these sentences?

C. It will be the first time that you meet your cousins.
D. It will be the first time that you will meet your cousins.

Are both sentences above acceptable?
If the second sentence is incorrect, is there a grammar rule in this kind of sentence structure?

Please advise. Thank you.
Comments 
Is there a difference in meaning between the sentences above?-- B shows more earnestness

Or is there an implied time for the verb between these sentences?-- No.

Are both sentences above acceptable?-- Grammatically, yes, but native speakers use C.

If the second sentence is incorrect, is there a grammar rule in this kind of sentence structure?-- Native speakers tend to use present for future in dependent clauses.
Thank you for sharing your thoughts on this. I now understand. Emotion: smile
I'd say:

C. It will be the first time that you have met your cousins.

Michal
Not really, Michal, because normally we 'meet' (= are introduced to) people only once.
That makes sense! Emotion: smile [Y]