I mean, technically you could use unsigned 32bit if you don't need to handle dates before 1970. But yes, the best course of action now is to use 64bits. The cost is pretty much nothing on modern systems.
I'm just cautious of people judging software from a time with different constraints and expectations, with the current yardstick.
I also wonder what the problem will be. People playing ghost recon in 2038 are going to be "retro" gaming it. There should be an expectation of such problems. Would it prevent you loading or saving the file is the question?