It sounds like that hidden version of Golf on the Nintendo Switch may actually a tribute to the company's late president, Satoru Iwata. A group of enterprising hackers (including "yellowS8" from our last report) discovered that unlocking it is limited to one day per year: July 11th, the day Iwata passed after battling cancer. You can't just go in and manually set your system clock, mimic Iwata's Nintendo Direct gesture and start hitting the links, though.
If you've ever connected your Switch to the internet, that's going to negate your chance to play the other 364 days of the year, according to the Switchbrew wiki. " The loaded date originates from network-time-sync'd time, regardless of whether the user has it enabled or not. When the system was never connected to the Internet, it comes from the user-specified date instead. This is loaded from the time service-cmds, with the actual time-sync being handled by NIM."
So if you want the chance to play the classic game on your Switch, it sounds like the only ways to do it are either buy a new console and not connect it to the internet, or, wait around until next July. You can also peep the video below if you'd rather not go to all the effort.