I would like to buy tickets for February 17th but can't click on it. Will they be available closer to that weekend?

Nearer the time

It's possible, but I think they only offer tickets for a certain number of days in advance because of weather changes. It could warm up in February and then they would close earlier. If it stays cold, they may stay open longer.

I think the 10th Feb is last day to visit for year 2018

Likely, but you can also walk up and get tickets.