Instead of a "yellow card", I call a little "timeout".
So, just out of curiosity could you tell me how long this is usually going to last
Solely my discretion.
There have been instances in the past where I deleted a negative after only one or two days.
In other cases, it took as long as three years.
I tend to go over my trust ratings from time to time, look into their respective references, look up an up-to-date post history of the rated user and make up my mind.
It helps if you keep reminding me of doing so after a while (say, a month or two), but please refrain from bugging me constantly about it, that'd just be annoying and might actually lead to a less favorable outcome.