I'm incredibly thankful that my wife is supportive. If I'm able to make this 4 month hike happen later this summer it will only be because she's staying behind and working while I do it. She'll continue to work while I build our new place this Winter, and then she'll join me in the Spring. If it weren't for that I'd still be working because I wouldn't be comfortable drawing down our stash, due to no income, while spending the capital to build a new house.
I added 5 months to my RE date (4/6 moved to 8/1), but have yet to announce it. I'd like to not go in tomorrow though, just be done. I have put so much energy into planning for RE that I feel like I am just ready to go. I have a very good job, but I want to go ride my bicycle for a few months, like you want to thru-hike the AT. I have always wanted to cross the country by bicycle (at least since I was about 13 or 14 years of age) and couple that with the desire to have an abundance of free time (just to soak in it) and that has built to be my main focus, out weighing staying at my job until August 1st. That being said, I may just go July 1 (I am FI already), you know since the passes in the Rockies might close early ;-). Gotta have your priorities straight!
On hiking the AT and deciding on FIRE. My situation may be the same as yours, just insert AT (and an extra month!) where I say cross the country. I might be able to put off my cross country ride another year, but I feel that planning on doing it this summer will significantly increase the odds of me actually doing it (not just my motivation, but for many other reasons that might be out of my control in 2017). So, you might want to consider my words and apply them to your situation about the AT. I've put it off for about 36 years (from an age that I could actually go out and do it ~ 18).
BTW - I'll likely be on the AT sometime after FIRE, as that is one of the things I want to do more of in retirement (6 days completed north of Asheville last summer). I just don't have enough vacations now to do all the outdoor things that I want to do (e.g., a week in the Mohave desert this April - definate, multiple days/weeks on the AT, weeks on my boat in the Everglades and Keys, ride around the country on my motorcycle, do the Great Loop on my 18' Panga Marine Skiff, take a train to Washington DC and then ride up the C&O/GAP trail to Pittsburgh then up to Ann Arbor to watch Michigan play Ohio State in 2017, oh and ride across the country later this year just to name a few : ).