The duration of an itinerary is counted in days (start to end date) and the leg in nights (departure to arrival date). That is because you may arrive on a Monday and leave on a Tuesday. Therefore, there can be confusion if you were there for one or two days, but it would strictly count as one night without any confusion.

Therefore, you would say you went on a 14-day holiday or trip (the itinerary) and spent 13 nights on all your legs combined, for example.

There is also an important distinction between planning (what's the intention) and estimating (what's calculated). A time of arrival is always an estimate as a calculation is required; that's why it is called ETA (Estimated Time of Arrival).

You can't plan to leave San Francisco and arrive in Hawaii 10 minutes later, regardless of how desperate your intention is. If you intend to arrive in Hawaii by a certain date and estimate 10 days for the journey, then you can plan to leave San Francisco 12 to 15 days before. Therefore, your departure date is planned (what's the intention), and the arrival is still an estimate (what's calculated based on season, winds, currents, and many other factors). Plans can change due to weather, government requirements, breakdowns, delays, etc.

The following tips are worth noting to manage your itinerary and maintain an excellent overview:

1. Name your itinerary with a short and clear title, such as 2025 Antarctic Expedition or 2025 Italy Family Cruise, that is descriptive, easy to remember, and simple to refer to in conversations.
2. You can set your itinerary's visibility to private while planning it, share it with only those you contact, or share it with anyone who views your profile.
3. Next, add each leg of the significant stopovers by date and location.
4. Then, keep updating each leg as required.

Be realistic and mindful when planning an itinerary. People will arrange their timing and life around it, taking time off work, booking flights, arranging accommodation, etc. It's crucial to let the crew know how accurate they can expect the itinerary to be.