<<"So that gives you almost 2 hours to catch your plane. But do check withthe airline until what time you can check in. If you're not comfortablewith the morning trip there are airport hotels nearby, so you can travel the prior evening.">>
I read your time and date as 12th of July (US style.) If you meant 7th of December, the tourist load at Interlaken should be lighter, although that is not too early in Winter to have occasional snow. July will have lots of tourists on the trains.
In theory, and in practice, that schedule should work, as long as there are no unexpeced delays of more than a very few minutes. Even though rush hour travel can generate heavy traffic on the rails, especially into Zürich and the airport, which can cause delays of up to 5-10 minutes, I have been able to arrive at the airport 2 hours before morning flights, or a bit less, and make my flights to the USA out of terminal E, but with almost no time to spare.
Two hours is what I have found to be an acceptable time on Delta flights to the USA. For flights at 9:30 and 10:30 AM, 2 hours ahead arrival at the airport has gotten me to the gate as boarding has started. So, there is almost no margin for error, and little or no time to shop for duty free goods.
I do have the advantage of "Sky Priority" frequent flyer status, which moves me through the lines a little bit faster, but I have to go to Terminal E to catch Delta Flights. And, Delta interviews every passenger for a few minutes for security reasons. If you are at the end of the line for economy class, or the short trip from train to check in desk is encumbered by heavy luggage or other issues, and your airline is slow at check in, that could be a problem.
Arno has made a good point. How much time does your airline recommed?
You can check in on many airlines, via internet, 23 hours and 59 minutes before flight departure. That assures that your immigration paperwork is in order ahead of time.
That can save a few minutes at boarding, but you still have to go through the lines to check your luggage.
And, if you are traveling with a family with children and lots of luggage, count on extra time. Kids need to use the toilet at the most inconvenient time.
The only way I would do that (and have done it several times) is if I were traveling by myself, and had fast moving luggage. And, I prefer to not be so far away from the airport, just in case something goes wrong.
And, as Arno points out, there are airport hotels. And, from Zürich main station, there are approximately 6 trains per hour to the airport. Trip time approximately 10-15 minutes.
I stay downtown, but I know my way around Zürich.