If you contact the collection agency and ask them if they will remove the collection remark from your credit report if you pay them off and you do pay them off then the collections remarks should be taken off your credit report within a few weeks to at least a few months after paying off the collections.
If however the collection agency doesn't want to remove the collections remark or you still fail to pay the collections off then the collections will remain on your credit report for 7 to 8 years.
After 7 to 8 years the collections remark on your credit report should not harm your credit rating unless you make contact with the collection agency after that time.