Though unreliable at times due to its servant of preference, the cirnopedia has the summoning schedule JP server had up to date, which can be seen here. As for events, this can also be seen in the site, yet providing less information about the events than other sites, here.
I'm basically #SavingForIshtar, not going for anything else. If I get her early, I may also roll for Memerlin, and if I don't, I'll go full McDuck and wait for St. Valentine 2019, for our best otaku.
This post, blue stands for a joke.