It may never show up, but there’s no telling…
Although there’s no grace period, it doesn’t necessarily mean that it is already on, or ever will get on your credit report.
First, not all collectors report to the credit bureaus. Second – they usually don’t report the item immediately. Instead, they hold off and try to use it as a threat against you, to try to make you pay them.
Usually they would try to tell you something like: “We haven’t reported it yet, but unless you pay us in full we will report it and then your score will drop”.
Every collection agencies act differently, so there’s no telling what this collection agency will do except wait and see.
Hope this helps