Quit Employer After GC

Gurus,
It will be 6 months post GC in a couple of weeks with my current employer who got me GC. I would like to lookout for new opportunities (which I havent till now since I hd no intention of quiting so far. So havent applied /interviewed anywhere) . My job is increasingly becoming untenable due to long hours required etc.

I realized there is no rule on when I can change jobs after GC, but would like to hear from the experts as to

a) whether there would be any adverse effects of changing jobs in the 7 th month after getting GC.
b) If there is a backlash from the employer (like I140 withdrawal etc) what will be the impact.

Just want to act out of caution so that I dont play spoilsport with my GC.

Seattlet,

a) If you were with same employer on H1 as well, 6 months is a good time-frame. It's just what I think as per my logic, it might sound weird mainly when you are applying outside of US and change your employer in few months. And even a lawyer won't be able to tell you 100% on whether 6 months is a good time-frame or not. FYI: Actually I joined the client, I was working for on H1, after like a year of GC.
b) Once you already have GC, then I-140 doesn't matter.