Keep in mind this is going to be for a 24 hours, not a sun up to sun down. So you will need to have competent watch keepers. If you are doing this with non sailors and want to keep it to daylight hours 70 Nautical Miles would be pushing it hard. Also can depend on the boat, bigger boats should be able to cover a bit more, smaller less.Iv'e zigged and zagged across most of it.
As a rule say 120 nms per day.