Multiple Web 2.0 create on the same day ?

Will it be harmful if I create like 3-5 web 2.0 on the same day ??

There is no log for 2.0 creation date. Technically you can go paranoid and be suspicious that, in case all 5 start to first rank the exact same day, SE could exact match this coincidence especially if all 5 link to the exact same places.
Since the algorithm is completely blackbox, it is really difficult to know how this could affect anything related (specially because noone can analyze this with precision).

Just a personal opinion, I'm sure 90% of the 2.0 rankers never thought on this issue, therefore, they created not 5 but dozens of 2.0 at the same time, and they are already using them. So if the technique itself can just work, then the probability that this is a footprint factor, is really low form a point of view. But as I said in a previous message similar to this, the worst part is that if you get flagged then you will not even know if it's because of this, or because they are really flagged my manual moderation or even other footprints... so don't mind by such little amount of sites.

I don't think that would be a huge problem. I've seen some of my colleagues create more and I don't think they encountered any issue with those.