Usually, if, while analysing a problem, a further issue appears, the further issue is only decided, if the answer to the issue is relevant for the analysis of the greater problem. Therefore, the first question, you should answer, is not, if the novel quote is supported or contradicted by the movie, but if the novel quote is really deciding for the question, how long the Tatooine-Alderaan trip was.
If the quote, even if it would have to be considered, can't really contribute to the answer of the main question, it is irrelevant, if the quote is to be considered.
And I think, the quote has only relevance insofar as we know from it, that the Tatooine-Alderaan trip couldn't have been longer than 1,5 weeks.
But it has no further relevance. I agree here with
- Isolder74, who wrote:Three weeks time might have had nothing to do with the travel time at all. Han probably just threw out a number long enough away to, as he felt, give him plenty of time to get to Alderaan and back and give him plenty of lead time to get all he needs done before hand. 3 weeks could havge just been an easy to remember number and nothing more. Remember with 15% interest it is in Han best interest to fly back as soon as he could to pay Jabba. 3 weeks could have been simply don't charge me anything for 3 weeks and I'll have it to you in that time.