How long does it take to repair a credit report and increase score for a negative item?

You need to add positive record in your credit report. Just paying off debt is not enough for increasing credit score. Try to manage your credit cards and other bills properly. Sty within your credit limit and make every bill payments in full and on time. This way, your credit score can increase. It takes time. You have to wait to see the result.

See, it's a wrong concept that your credit score will increase after paying off debts. You have to add positive information in your credit report to see a positive effect on your credit score. Keep on adding positive information on your credit report. It will help you to raise your credit score. Also, check if there is any wrong information on your credit report. If there is any wrong information, then try to rectify it asap.

Check your credit report for errors, that's the first thing you need to do.
Then, try to add positive info as suggested by David. You may pay your bills on time, or take out new credit and use it wisely.