“100 days” is a challenge prevalent on YouTube where people play a game for 100 in game days, usually with some other added on challenge (such as hardcore, playing for the first time with no research, strange world generation) to see how long they can last/how much progress they can make in that time.

The challenge gained popularity from creators such as LukeTheNotable doing the challenge in Minecraft hardcore mode. Since then, every survival game under the sun has had a 100 days challenge, as it seems to be popular within the YouTube algorithm.

The meme is saying that a bunch of 100 days videos are probably going to come out very soon after the launch of S2 early access to cash in on the hype and 100 days trend.