Ask HN: Change job after short time?

I recently accepted a new job in a small startup and after arriving I found that their focus had shifted some since the interview. In their view, they are focusing on a different (related) detail while the 'big picture' goal is moved further down the timeline. Otherwise the company and people are good, I'm just disappointed because i'm not doing what I expected.

Then by coincidence I got a call from another company that is doing very much what I want to be doing. It's an amazing offer and I'd love to work there, but I feel an obligation to the current company.

Is there an obligation to stick it out for a year (or some other amount of time)? I feel like I'm already counting the days until I can jump ship. I've never stayed less than ~3 years at a job before this one. The other is offer is just too perfect for my personal career goals that I would be willing to break norms in this case.

Happy to hear some other feedback.