I've done plenty of road tripping myself, all over North America, and I think I have some idea of what you want...
Back in the bad old days, before Google, a "map" was physically printed on paper, and there were entire books you could buy which had maps of various parts of the geography of a country, as well as a section showing the distances between various towns and cities. I hear they still exist.
By knowing the distance you intend to travel, you can fairly well estimate how long it will take. Try this experiment: Drive from Montreal to Sherbrooke, at an off-peak time of day. Note the time you start and end, and the distance you travel. You should come up with approximately 90 minutes and 150 kilometers. If you check Google Maps, it will suggest a very similar time and distance.
Knowing this, you may consider a rule of thumb that you can travel 100 kilometers in an hour on an autoroute (or Interstate in the US). Let's call it 60 miles, since the US is still a backward country that hasn't quite adopted the metric system. This seems like a very good estimate, in my experience.
Now, drive back to Montreal and this time, don't use the autoroute. Use the smaller provincial highways and back roads. Again, you should come up with 150 kilometers, but this time it will take two and a half hours! This suggests that you can estimate your overall speed on such roads at 60 km/h (or 35 miles in the US). This also seems like a good estimate to me.
Similarly you can figure out how much time it takes to get off the highway, fill your gas tank and get back on the highway (maybe five minutes; not long enough to worry about).
You must be hungry after all that driving, so find yourself a diner! Note the time you walk in the door, and the time you leave. Depending on how quickly you're served and how quickly you eat, this may take you anywhere from 30 minutes to an hour. Repeat this at several other restaurants, and get a sense of how long it takes you to eat, how long it takes you overall at different types of restaurants, etc.
Crossing the border (usually 5 to 60 minutes, depending on traffic). Not much more to be said about this.
What remains to estimate is how much time you want to spend at various attractions. For this, you'll first need to figure out what you might want to see and do.
For instance, you might wish to drive the Kancamagus Highway. You can do that in ... by our estimate above, just under an hour. But there are several places along the highway that you might want to stop and look at something. That might take you five minutes, or you might be inspired to stand there and watch a waterfall for hours. Only you know for sure.
One thing I will advise you not to do is to plan your trip with strict adherence to a schedule. It sounds like you might be tempted to do this. On a road trip especially, you will often run into something that you want to stop and spend some time looking at, and if you feel rushed, then you might not do so, even if you actually had plenty of time. And even if you do run short on time, Quebec is not that far away...
If I were going to give you a nice rule of thumb, I would say to figure on 12 hours for your evening meal, sleeping, getting up and having breakfast. Then about one hour driving for every hour doing something "touristy" ... give or take. You might decide to stay a couple of days in some town, for instance.
If you're still not sure, find a couple of tourist attractions right in your city and visit them. See how long it takes. Most people never do this, which is unfortunate for them...
