marinading duck legs - but how long is "overnight" exactly?

[ZingChoirsOfAngels]

a lot of recipes suggest marinade overnight (so I'd think about 12 hours) - but if you place the meat in the marinade in the evening and only use it the next evening it's really a 24 hour business, isn't it?

what's your guess/knowledge on this?

btw I'm making duck confit and started marinading the legs at 10 am.
I'm not cooking it tonight- I think tomorrow morning will be fine.

I always assume that if a recipe says 'overnight' then exactly doesn't matter and that overnight is a minimum.