How long does it take for your FICO score to rise?

After paying off/finishing a lease on a vehicle? Also after paying off a financed vehicle? How long does it take for your score to rise and by how many points? I make my payments on time all the time (sometimes even 4-5 months ahead of time) and I do wonder does this impact my score even more. My husband and I are steadily trying to improve our scores (I am at 540 and he is at 544) so we can purchase a home in the next few years. We know to even be qualified for a home loan our credit scores need to be above 580. We regularly check our credit reports to see if any information is incorrect so it can be disputed. We were wondering should either of us get a secured credit card just to add on and show lenders/financial institutions we have a good payment history? Any advice/suggestion is appreciated. Thanks.