Garden plants have this annoying habit of ripening when they want to - they don't even bother to ask me when I would find it convenient for them to be ready! This problem is especially exaggerated for those of us who want to can our produce but are working with smaller suburban gardens.
I have found an excellent solution to this "problem" for tomatoes! Throughout the summer, as my tomatoes ripen, I slice the tops off of tomatoes that I want to can into a sauce or diced tomato and throw them into a freezer bag in the freezer.
Then, when I have enough tomatoes to do a batch of canning, I pull the tomatoes from the freezer and drop them into lukewarm water. Given a few minutes to thaw, the tomato skins will slip right off in your hands and you are ready to begin the process of preserving them!
I love this method because it allows me to only pull out all of my canning supplies when I have enough to be as energy efficient as possible by canning a full load of cans, helps me not to waste any of our produce because I can can all of the tomatoes that come in regardless of whether they come in at the same time as many others or not, and because it allows me to put off canning until the cooler months when the heat generated by the canning process helps to heat (rather than over-heat) our home.
This solution works great for me....I hope you will give it a try if it could help you to be more efficient in your preservation efforts as well!