[meithecatte]

I'm pretty sure this is a feature that's available at least to big creators – I remember a Tom Scott video doing a bit involving scheduling an ad at a particularly fitting moment.

You might have to be a YouTube partner or something like that to make use of this stuff, though.

[jonas21]

You need to be in the YouTube partner program, but that's not just available to big creators.

You need at least 1000 subscribers and a certain amount of video watch time per year to qualify, but even fairly small channels can meet this bar. When people talk about getting monetized on YouTube, this is what they mean.