Cats' long-term memory can reach around 16 hours, but this isn't absolute; sometimes it may only last a few minutes. This mainly depends on whether the cat's attention is interrupted, similar to how humans forget what they were trying to remember when their attention is diverted. Of course, cats also have short-term memory, the duration of which is mainly affected by the testing method and individual differences among cats, and may only last from a few seconds to several tens of minutes.
In fact, cats' memory has a unique characteristic: it is highly interest-driven. That is, cats are only likely to remember things they are interested in for a long time; they simply won't bother trying to remember things they're not interested in.
