How long lasting is the blood thinning effect of ibuprofen (advil)?

Very short. Probably as short as 6 hours. Definitely less than 1 day. As opposed to Aspirin which takes a week to wear off.
Not long if lucky. If you do not develop rare but possible life threatening issues from the drug and you are speaking of the "anticoagulation" effects sort of like aspirin, it is a weak anticoagulant and only lasts a few hours after the last dose.