I sent an online application for a job. The job description specifies as a requirement experience using library "a" (programming language "A"). Although I don't have experience using library "a" (I do have some experience with language "A"), I applied anyway because it is similar to another library I have used, library "b" in programming language "B".
A few days after I applied (fewer than I was expecting) I received a response from a person in HR stating that experience in "a" is required, and that I should include some samples of that work in the application (as an e-mail response). I did not reply to that e-mail, thinking I didn't have a chance on that job anymore.
Two days later, I received another e-mail from the same HR person. This time that person sent a test (some sample data to work with), and that I am encouraged to reply directly with my answer to the test. A time limit was not specified, but it specifically says that it needs to be programmed in using "a".
However, this was two days before I leave on a 10-day holiday, where I will not be able to work on this test (I won't even have access to a computer). Between the time of application and the second e-mail (6 days) I had been studying how to use "a" effectively (for personal study, not for this specific job). When I received the second e-mail, I decided to give the test a try, although I wasn't expecting to finish it on time before I leave. Anyway, I will try to finish it when I come back. Given my current knowledge of "a" (I am aware of the Dunning–Kruger effect), I estimate accomplishing the task in about 3 days after I come back.
Before I move on to the question, some final background information: I am a PhD student and my resume clearly states my expected graduation date (also, it does not say that I have experience in "a"). Therefore, I would expect the recruiter to think that I will work on this task during my free time (and that the person already knows I don't have experience in "a").
Now to the question.. when I finally finish this task, it will have been at least 15 days (2 + 10 + 3) since receiving the task. Should I let the recruiter know about the cause of this delay? If so, what would be the most professional way to do it, and when should I do it?
Option 1: I reply with my results whenever I finish and don't mention anything about the time I took to do it and/or the fact that I didn't have any previous experience with 'a'.
Option 2: I reply with my results whenever I finish and subtly/professionally explain why I took so long to do it.
Option 3: I let the person know in advance about the delay.