How Long Does A Flea Collar Need To Stay On A Kitten?

my cat is about 6 months old. she got fleas on her today. i was told to keep her in the house until the medication would take effect and then put a flea collar on her. how long do these collars need to stay on? I have not found any information that tells me when they will work or just treat for one day after using it.. Is this something you can tell me by email? I am not sure what kind of information you are seeking regarding your question but please be specific with your questions so that we may help you better!