This month banners

F2P but planning to get both Merlin and Jalter? I'm sorry, but unless you have thousands of SQ saved up (which is highly unlikely considering you've only played for 20 days), that's not gonna happen (and even if you have thousands saved up, it's still very difficult to get both).

My recommendation is to go for Jalter if you're in dire need of DPS Servants, but if not, just go for Merlin.

And to answer your question, Jalter and Merlin will both be available next year on the paid gatcha.

However, if you want to remain F2P, then Jalter will be on rate-up 2 years later during the Da Vinci event re-run and Merlin will be on rate-up next year during the 10M downloads campaign.

I recommend you just go for Merlin in the long run if you're F2P. You could feel free to try for both but you'll need extreme EX rank luck for that type of miracle to happen.

Both Merlin and Jalter will only be available for free once more each after this year (at least based on what JP has gotten so far - we will likely get more in the future), Merlin again mid-late next year and Jalter in early 2020. Both are available in a few paid gachas after this though.

To the best of my knowledge, to get a 1/2 chance of getting either of them, you'll need to spend about 300 quartz on their respective banner.

If you've only played for 20 days, I'd suggest catching up with the story and doing as many free quests as you can to get all the saint quartz, and spend maybe 100 - 200 (max) for Jalter. By my calculations, we will get around 100 - 200 free saint quartz (story missions, events, login bonuses, etc) from now until Merlin's release, which should give you a decent shot at him.