It usually takes 2,5 days but you can use glucose disposal agents and reduce the duration needed.(ALA,chromium,cinnamon)
It also deepends on whether you perform any heavy anaerobic exercises as well because it forces you becoming faster glycogen depleted,thus entering to the state of ketosis faster.(weightlifting-high intensity cardio do the trick)
I highly recommend you lowering your carb intake to no more than 20g. per day.
As for your last question,well,be more specific.If you consume a ton of carbs,it's gonna take you a lot of time (2-3 days) to re-establish ketosis.A small overdose won't interrupt ketosis but only for some hours.