How late is too late?

[Peppermint]

I've got a lonely duck egg on day 30--a Blue Swedish. I candled at lockdown and it still had a bit of fluid left. I candled again on day 28 and there were no light areas, intact air sac and I saw movement. I've been staring at this egg for about 5 days now and am losing hope. I periodically check for peeping, but it appears that the duck hasn't internally pipped.

So...when should I toss this egg? I've only hatched chicken eggs, so I'm not sure if the duck incubation range goes much beyond 28 days.

Thanks for any wisdom.