How long was Blackbeard at marineford?

[Warmmedown]

Did nobody sense him with observation haki? How did he even get there? Did nobody see the activity of his ship? Did he have a ship or just a little boat or raft?

 

[SSJ2]

Nobody sensed Shanks either. They can probably control the level of Haki they are putting out.

As for how they got there I think it was said they stole a Marine ship from Impel Down.

 

[Symbiote]

They didn't sense Whitebeard either until his ship popped out the water.