Two simple principles of biking tell you how to ride a tour when you haven't trained ahead of time.
1) Ride according to how you feel. If you feel like continuing to ride, keep on riding.
2) Once you have ridden 1000-1500 miles, you can ride a century everyday for the rest of your life.
If you feel like riding big miles one day, do it...if you don't, don't. Listen to the body.
I had a day on 2015 trip where I was planning around 125 miles one day and then 100 the next. I got into town for the evening and had resupplied for the next day and went to go looking for the campsite for the night. As I left I found the worst pavement I have ever ridden on. I couldn't take my eyes off the road, it was in such bad shape. I passed by a couple of the possible campsites as a result of riding past them while trying to not get 'lost' in the horrible pavement. I knew in no way at all would I ride that stretch of road after dark. I knew I had one more campsite which I figured would be a winner. I didn't realize it was that far out of town. As I rode more and more toward it I thought about changing up my normal evening routine. By the time I got to turnoff for the campsite I had already made the decision to combine the two days into one. I was feeling great and I knew the forecast for the overnight was to be lows in the mid 50s(I knew that would help to keep me awake for the overnight ride). I said the heck with it and decided to pull the 227 miler for the trip and kept on riding and finally pulled into my moms house around 5AM. It was one of the nicer rides of the entire trip.
Don't let yourself be rigid in your trip plans. They will never go according to schedule. Be willing to explore, even the human limitations you think exist, you might be surprised at what you can do.
I saw here on the forum back in 2013 a discussion about the three most pivotal days of a bike trip. Day 1, Day 3 and Day 12. I couldn't agree with that posting more, other than to say there are more days, further out which have an even bigger impact on things. I have experienced it and have heard other people talk about when they have been interviewed on podcasts. The body goes through an amazing transformation when you give it the chance. You can go from not having been on a bike in ages to being able to ride higher mileages consistently, even touring, in a relatively short amount of time...as long as you keep at it constantly everyday.
The more rigid you make your trip plans the less room you have to maneuver when things don't go according to schedule. Learn to be flexible in your thoughts on how the trip must go. Better yet just go ride and only plan from one day to the next. I quite often change my plans midday even when I see something I wasn't expecting and want to stop to explore more. If that causes me to not to get into town until after dark...so be it. If enough things go wrong than I may very well change where I was planning on spending the night and learn how to wing it. This is the one reason I like not spending nights at hotels/campgrounds/hostel/etc. I can go wherever I find a place to lay my head for the night and I don't have to make a specific destination.