Just a small note that your ability to contribute via research doesn’t go from 0 now, to 1 after you complete a PhD! As in, you can still contribute to AI Safety with research during a phd
I think you should consider more options besides PhD research and engineering.
For example, working at orgs. Or switching career paths entirely to something much more needed, such as computer security. Or joining a startup.
Apply to orgs when you apply to PhDs. If you can work at an org, do it. Otherwise, use PhD to upskill and periodically retry org applications.
You would gain skills while working at a safety org, and the learning would be more in tune with what the problems require.
I can empathise with your situation. Although I am not making career choice between engineering and research, I am looking to decide what to work on next.
I cannot give you any answer, but I can share few heuristics I use in order to decide what to work on.
For one, you are asking how should timeline affect your decision. But I would consider other variables that might affect it as well and I wouldn't place too much emphasis on only one, e.g. time in this case.
You have advantage in having binary choice here between engineering and research. So I would ask, from which it is easier to transition into the other? And which gives you more opportunities in the future?
Making decisions now based on our predictions of unpredictable future is maybe not the best way to go about it. So consider that if your predictions about future go completely wrong or in unanticipated way, which choice would be more robust?
Also if you are anything like me, deciding mostly on what you enjoy now wouldn't be very wise as what I tend to enjoy does change with time and new experiences. So I prefer choices that give me more options and easier transitions in future.
Hope this helps!
Another heuristic is to choose the option where you're most likely to do exceptionally well. (Cf heavy tailed impact etc). Among other thing this, this pushes you to optimize for the timelines scenario where you can be very successful, and to do the job with the best personal fit.