It will be used in a tabular data program to show information about free work days of employed and each column can't have enought space to include full week day name. For "common form" I mean, what are the abbreviations that is more used in programs.
word choice - What are the abbreviations for days of the week ...
Words exist to label periods of time - like week which represents 7 days and fortnight which is used for a 14-day period. Are there other such words used for certain numbers of consecutive days?
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
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 ...
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.