Everything on a save the date is a promise a guest will hold you to, which is why the short version is also the safe version.
Do not name a venue you have not booked. Guests look it up the same evening, price a hotel near it, and remember. A region is a safe promise; an unconfirmed venue is not.
Do not commit to a ceremony time you may still move. On a printed card that means leaving the time off altogether: it is exactly the detail a guest will screenshot and never check again. On a link it means treating the time as provisional — the details strip shows the time you have so far and the add-to-calendar button uses it, you can change it later on the same link, and you can take the time row off the page entirely if you would rather not show one yet.
Do not ask for a reply. An RSVP on a save the date collects answers from people who have not seen the venue, the time or the schedule, and you will have to ask them all again anyway.
Do not mention gifts. It is early, and it reads badly at any stage.
And one thing to be sure of before it goes out: everyone who receives a save the date must receive an invitation. There is no polite way to take it back, so the save-the-date list is the moment the guest list stops being a draft.