Ho-oh was initially scheduled to end tomorrow, the 12th. But, people were having network issues with not receiving raid rewards and not even getting a chance to catch Ho-oh after beating him, which meant people lost their raid passes and came out of the raid with nothing. So, I'm pretty sure Niantic extended the deadline to the 14th now.
GamePress
When does Ho-Oh's term as the legendary raid boss end?
I think Ho-Oh's term as the legendary raid boss was originally scheduled to expire today, but the term was extended by some small number of days. Does anyone know when its term is now scheduled to end?