I am going to make up three sentences below.
(1) Three weeks ago, I was writing a short essay for five days.
(2) John was scoring a lot of goals for many years.
(3) During Tim's one-week stay in my home, I was working on my project for five days.
I am using the past continuous tense because the action mentioned in each sentence happened over a period of time. Does this tense work in my examples?
One sentence suffers from clarity issues, while each of them could be cleaned up to sound more natural, as well as for readability.
Regarding your first sentence:
This is essentially clear. There's not much else it could mean beyond there being a point in the recent past during which you spent a five-day period of time working on an essay.
Written more naturally, it would be:
Three weeks ago, I spent five days writing a short essay.
Or:
Three weeks ago, it took me five days to write a short essay.
As for sentence number two:
This one needs some clarity. Are you trying to say that John was a big goal-scorer before, but now things are different? Are you saying John scored a lot of goals until something happened to change that? It's not obvious what the sentence is trying to say, but here are some options for a rewrite:
For many years, John scored a lot of goals.
Or:
For many years, John had been scoring a lot of goals—until...
Or:
John had scored many goals over the years.
Without context, though, it's impossible to determine which best communicates your intent.
And then, sentence number three:
Again, this one's pretty clear, but awkwardly worded, which impedes its effectiveness.
A different option:
During Tim's one-week stay in my home, I spent five days working on my project.
Or:
The week Tim stayed with me, I spent five days working on my project.
