I'm sorry. The tense you used in your example is too complicated for me, so I'm still confused.Two days longer.
Two more days is used when you are referring to something that is/was already taking place:
I had been waiting three days already when Amazon told me it would take two more days.
Thank you so much for the detailed explanation.No, it does not matter whether it is in the present or the past in respect of now, but what whether it takes place before or after the time you are describing in the sentence.
In your example, the sentence is set in the present and you are looking back to something that happened in the past, so you use 'two days longer'.
If, instead, you are looking ahead to the future and the thing is already happening, use 'two more days'.
The weather forecast says it will snow for two more days. (It is snowing already)
If the thing isn't happening at the moment, you use 'two days longer' even when looking ahead.
Next year's holiday will be two days longer than this year's.
You can set a sentence in the past and look ahead. This is what I was doing in my earlier post, to give an example of using 'two more days' in your original situation. I did not mean to confuse you.