Board Thread:Questions and Answers/@comment-26042064-20170719111636/@comment-202.67.41.234-20170719113949

Sure, you can keep it without any problem. But it will expire after the campaign is over, which is in a few days; just look at the selection and see the 'Days Left' or something.

This isn't some magic ticket to guarantee Okeanos era and above 4-star Servants, it's to jumpstart your roster with what you have now. I suggest you pick something in the next few days; if you don't, the ticket will expire and you get nothing.