> How long do I stick it out before looking elsewhere or even returning to my last job as I left on good terms?
Eject, as long as this isn't going to add to an existing pattern in your employment history.
People in the position to hire have more than likely been in the situation where they were sold a bill of goods, gotten on the job, and had to make the same choice.
But if this is going to be, say the third short term gig in a row, then it's going to be a hard sell that the problem has been the employers and not you.
Assuming it's the former, when it comes time to talk to other potential employers and interviewers, state the scenario factually and without rancor. "I was told during the recruiting process that we would be writing the platform in Node, turns out we were hand punching Fortran cards."
Edit (hit submit too soon): if it's the latter, then you need to stick it out for at least 12 months. There are some great comments in the thread about changing the culture, etc. I would add to those to shift your mentality from "this is my employer" to "this is a client for whom I'm going to do the best work I can for 12 months." I can yap a lot more about that shift but if you can create a mental firewall between you and the employer and minimize emotional engagement, doing the time will be easier. :)