as others have noted your draft
is a huge concern. a typical 47' boat drawing 8' or more must be very careful in those mostly shallow frequently badly buoyed waters. if you are not a very experienced sailor I would work with a local to lay out a not too stressful sailing plan and follow it closely.
as for your question, you need to get very familiar with the local charts
. then it is real simple to lay a string covering your planned course to measure an approximate distance. then apply an assumed speed over bottom say 5 to 8 kts to figure sailing time. with kids
on board figure lots of stops/detours to keep them entertained so 8 hours/day may be optimistic.
exercise caution and it should be a great trip.