Balancing an internet startup and a tenure track professorship

Nothing is impossible, but how many hours a week do you want to work? Do you have any life beyond these two endeavors. I don't participate in a startup, but at various times have published books and software and built interesting tools for students and professionals.

But the warning here is that beginning a tenure track (especially) is a very time consuming proposition, especially if you want to actually attain tenure in a few years. You need to serve the students well at what ever level you find them. You need to establish an appropriate publication (research) history as well as a recognizable place in the profession through conferences and such. You need to have, or create, contacts with other researchers to help you in your own. This might come at your own University, given a large enough faculty with good synergy, but you may need to expand your contacts outside.

In the US, the typical "slog" to tenure is seven years and you don't get do-overs. Not every paper you submit for publication is necessarily going to be accepted.

You can read other questions on this site to learn some of the other problems that junior faculty have in adapting to the academic life. Not much of it is likely to come easily to you if you are really new at it. Good things happen in Academia, but they don't happen on auto-pilot.

Some institutions have a history of tenuring most candidates. Some, alternatively, have a history of tenuring nearly no one, though some of the "failed" candidates have a good chance of success in moving, due to the reputation of the university.

All that said, many (most) junior faculty do have outside interests of various sorts that take some amount of time and effort. It isn't impossible to succeed at both, but you may need to set parameters for yourself and decide early on what is the most important thing in your life. If you sort of stumble along at both, you aren't likely to be a success at either.

Finally, what you learn and what you do in the startup may be a plus when it comes to tenure, though you indicate it is a different field, lessening the possibility. But if entrepreneurship is valued in your field it may be a help.

I have done both, and let me tell you it boils down to how hard you want to fall into entrepreneurship.

I did research for my own sake and did teaching, to see students smile when their code compiled; but let me warn you with peace and love that both startups and doing research/teaching are both very stressful. So:

If you want to be serious about startup, you will eventually be very busy with it and not so much time doing research. However, if you want to use "I'm part of a startup" just to open a presentation or conversation then you can do both.

It might sound harsh, but you have no idea how hard a startup will be, both in terms of operations and people management.

What is 'Impact' anyway? Lets consider the word "impact" that you mentioned. What is it? Well:

Researcher: if you are a researcher it is very simple: the rank of the journal you are publishing shows the impact of your work. There is a difference if I publish my work as a poster in a conference, or publish it in a journal in THE Nature.

Startup: What is the impact here? Well, do you remember the "Green energy" back in 2005-2006; "social network" in 2007, "the cloud" in 2010, or "Big Data" in 2012; or "Crypto" in 2017? What all these things have in common? The fact that someone decided that they are the "next big thing" and the rest are following. Why the are following? Well they can get funded easier if they are "crypto-based" startup back in summer of 2017. The game is to get funding by promising an impact. Who and how they can deliver this, is totally different thing and in most cases, they are BS.

Philosophical: Lets think about this philosophically. You could create the better toilet paper, and have an impact everywhere, is this something you are looking for? You could write a research paper that most people or no one in your field cares. At the same time, you could get funded and create a successful or unsuccessful startup. What I'm trying to say here is that: you could succeed or fail at anything, at least choose something that you look forward to; so you don't switch as soon as you fail.