How to find out my date on this minecraft server? (ip: play.redstoneoinkcraft.com )?

Unfortunately as from what I know of, I don't think there's a way of finding out the date. However, your chat logs might be able to help you out.

Open the "run" program on your computer. Then, type this: %appdata%/.minecraft/logs

If you remember the month you joined, try searching through each day of that month and see if you will find something.