Heading to Vegas for ME, how late can I buy a seat?

[dlpnyc21]

My flight I scheduled to arrive on Thursday night late. Can I still head over to the Rio and register for the ME that starts on Friday? I call the WSOP hotline and I can't get a human being to save my life. Any advice appreciated.
I am specifically asking if I show up at the Rio at like 1am on Friday morning if there is still a way to buy a seat.
Thanks,
dlpnyc