This guide applies to all four of the medal achievements.
I think you now need to buy a month of premium to access the later challenges. I tried the date change method and the medals did not add to the counter. (Plus, premium lets you get the medals twice as fast, so much more efficient)
Go to this website for the solutions to the challenges: https://solutions-microsoft-solitaire-collection.com/daily-c...
And start back at January. As the year progresses, the guy seemingly gets quicker at solving the challenges. (He gets better at Solitaire) so I'd do January and February with Bronze medals, March and April with Silver medals, May through November with gold medals, and December with a Diamond. A gold medal CAN be achieved by doing them all in order, but that is simply not the fastest way.
In this section I'm referring to the length of the video solutions that you'll be following for the challenges. Spider and Pyramid tend to be the longest ones. Some spider ones are upwards of 5 and a half minutes, with the longest one being 11 minutes! Pyramid is generally around 2 and a half minutes, but what makes it as bad as Spider is because there's never rarely an "Easy" (Short) one that is less than a minute and a half, and they can reach up to four minutes. So, logically start at day one of a month and before doing a challenge, check Spider and Pyramid. If they're longer than you wish, say 2 minutes and 50 seconds or above, you can just move onto the next day, and forget about the other challenges, even if they're short. However, if you see a short expert challenge around that you want to snag you can do that since they give a lot of points, or also if there's a longer one that's about 3 minutes and is an expert challenge, just go ahead and do the whole day. You can skip several days in the month and still get gold, so try to avoid the long ones. Like I said earlier, Spider is the crucial one because it can be as low as 40 or 50 seconds, but can range up to 11 minutes. So that's the one you'll most likely be checking to decide whether you want to start a day.
One more tip for this, it is extremely helpful to play the videos on 0.5 speed, so you can just follow what the guy does and never have to pause the video. This makes it progress twice as slow, but ultimately is faster since you're never pausing. Once you get better, and you will, you will be able to almost predict what the guy will do since you know what the logical best move is. Once you get to this point, you can play the videos on 0.75 or even normal speed.
ALL of the medals took me about 60 hours. (12 bronze, 10 silver, 8 gold, 1 diamond)