6.5 hours my longest time doing any activity, so I will be doing a little more than double that if all goes well on my ride.
What I wanted to know is whether you have years of aerobic base. In other words - either an active life due to career - or lots and lots of aerobic hours. Just because you may be able to complete a double - doesn't necessarily mean it will be good for you - or help in your tri aspirations.
The fact that you have a family, you are attempting an extreme distance - early in the year - are all warning flags. These are all aspects that compete against success - at least usually.
But hey - if its a "beauty day" - if you have a good night's sleep - if your wife is happy to see you "go for it" - then try it. But if you are really interested in "building a base" for the long run - I'd suggest aiming for 150 miles - let's say in then hours - and then making a special effort to
eat and rest and recover properly afterward.
I know something about these things - and have seen smart people hurt themselves on rides that produce little glory - and even less satisfaction. And I know what it feels like to ride 200and come home to house of sleeping people and not have time to eat or recover or unwind. Good luck - you'll need at least a little.