Hello all users!

I will have to pester you with a few more questions about the General Data Protection Regulation.

Below, I have given a few variants on the same sentence.

What I would like you to do is tell me which of them is the most appropriate. Please notice that in the original I used "for as long as", not "as long as".
(As far as I know, "for as long as" does not always mean "as long as". My variants are time-related and have nothing to do with "if" or "for the reason that" meaning.

Could you help me to determine the best possible variant?

In my opinion, the remaining 3 phrases such as "throughout the time that", "at the time that" and "during the time that" are all synonyms for one another.

Data needed to fulfill the legal duties will be made use of by us:
a) for as long as the duties are done, for instance, issuing invoices or other documents that constitute a basis for settlements between us,
b) for a period during/in which regulations tell us to store data, for instance, tax-related data,

a) throughout the time that the duties are done, for instance, issuing invoices or other documents that constitute a basis for settlements between us,

or

a) at the time that the duties are done, for instance, issuing invoices or other documents that constitute a basis for settlements between us,

or

a) during the time that the duties are done, for instance, issuing invoices or other documents that constitute a basis for settlements between us,