Just bought it. Its really difficult to do. I can't really spin the card and catch it with the other hand. Does anyone of you have any advice oh how to do the trick? Or is there any video that teaches it?

my advice is, jus practise spinning without causing much tension.
catching is basically common reaction,.

Since someone brought out the topic of hummer card, how long can u maintain the spin on average?

hmm. im not sure for mine.
define spin.
from start till it stop moving?

Difficult spinning from one hand to the other? Then just make it spin away and back. You can use the same hand then.

I have problem getting it to spin around me convincingly.

i have problems making the gimmick last