Last month I took a 6-day trip to England to help take care of a friend who was in an auto accident (okay take care of her kids and house and take some pressure off her husband; the doctors were taking care of HER). It was really important, and not something I could really do with a 2 1/2 year old in tow.
Six days - I loved the time away, loved talking to my son on the phone, felt like I did a really good thing, my DH never saw any change in our son’s behavior, and when I got back, my daycare provider just about fainted from releif! My son went through a complete personality change - but ONLY at daycare. It wasn’t visible at home. He was miserable and confused, and was acting out all over the place.
If your fiance isn’t going to be doing full-time care, make sure you also check in with the daycare/preschool. They’ll pick up on issues long before they show up at home.
My recommendation is this: Plan for a week or at most two weeks away, check in periodically, and be prepared to come home early - WITHOUT resentment - if it is indicated. Vacations are flexible. Maybe you can take another week later on in the summer?
AND THEN, arrange nights off, at least once every two weeks, FOR THE REST OF THEIR CHILDHOODS. If you have relatives nearby, can they take your daughter overnight twice a month? Honestly, I’d go nuts without our weekly night off, and every two weeks is the most that is comfortable, and that’s without being pregnant besides. If you can even get an evening out, taking a walk, or catching a movie, that does amazing things for your relationship, your sanity, and your parenting! (Plus, if grandparents are handy, it gives them the chance to develop an independant relationship with their grandkids) Later, you can use this time to talk about how your kids are doing in school, or other parenting stuff, without little ears nearby to hear. It still qualifies as a break. If you haven’t had this kind of break on an ongoing basis, I know why you wanted the whole summer! Go for a structural solution, and hire yourself a babysitter, a family member, or whatever. Some daycare providers will also sit the kids they know, so you don’t have to screen a whole new set of people.
Good luck!