Woah, buddy. Calm down a bit. I see there might be a story and that you have the best interest of people in mind when you say this. But slow down and read the whole post maybe? Look at this like right below the expectations..
I understand that you are trying to help, but this is clearly meant for people who are not looking to make a career, at least not for now. They say it's for fun and their responses and posts show that they really are just trying to assemble a team of people who they can work with, for fun. Like a discord community.
There are even minors in their team as they mentioned which just puts more emphasis on the fun part. There are a lot of people below 18 who are looking to make webcomics and such, as you can see from the hundreds of other posts in the collaboration category.
As far as setting deadlines go, I don't see why one shouldn't do it?
Of course, it's for fun, but if you are planning on publishing your work or even doing it as a hobby while working with others, some degree of professionalism is important. They clearly mentioned realistic deadlines, basically something that fits the artist or whatever position someone applies for.
Again, I understand you are trying to help and conveying your experience, I am grateful for that. But you are coming off a tad strong, it might scare some people away for whom this might be a real learning opportunity.