This same question was recently asked by you on English Language Learners wasn't it? I believe the answer there was that none of them are correct because all of them should say, "the Internet". Once that is fixed, then the only viable sentences are the ones that use "for the last few days", "in the last few days" and "in a few days". Although the meaning of the last one is different.
adverbs - The variations of in/for the last few days - English Language ...
Is if you're treating the two days as a single length of time; are if you're treating them as multiple lengths of time.
Two days "is" or "are"? - English Language & Usage Stack Exchange
In most organizations, vacation days are usable at the employee's discretion, up to a certain yearly limit. Days off is a more informal phrase that includes a variety of kinds of paid-not-to-work days, including sick leave, maternal/paternal leave, floating holidays, national holidays, etc. Vacation days are a subset of days off.
"Vacation days" or "days off" - English Language & Usage Stack Exchange
It is a bit ambiguous but, given that the system would not allow you to complete the form 12 days before your planned arrival, the 7 day period is obviously a maximum rather than a minimum. The system will allow you to complete the form so long as the lead time is seven days or less. You can complete it six days in advance but not 8 days in advance. The reason for "fill in" rather than "fill ...
Fill in your application up to 7 days prior to your arrival