SPROUTING THORNS TIMELINE
I haven't been paying full attention to the seasons and moon-paces of the chapters when I first started, but now the story is more important to me than the simple "background thing" it was before, so here is the official time + some edits that I had to make!
SEASON:
Greenleaf [Chapters Quiet Here--Clanmates] (Two moons, making the months most likely July--August, or possibly August--September)
Leaf-Fall [Chapters Clanmates--??]
BREAKS IN TIME:
After Myrtlewing meets Nightfly, half a moon passes and they meet again at the gathering. This is where Myrtlewing's plan starts its formation.
Another half-moon passes when the Half-moon meeting takes place, and Myrtlewing goes to WindClan to speak with Nightfly. This is also the same time Alder starts bonding with Hootpetal.
Another half-moon passes between this and when Myrtlewing kills Fleetsong.
Another half-moon passes after Alder discovers Myrtlewing's murders and commits his own. He has been avoiding him for this time before deciding that he had to see it for himself to stop his spiraling thoughts--when Maplefall interrupts them by giving birth.
There! That's the part I had to fix--Maple got pregnant just before Myrtle met Nightfly, and I realized that she gave birth too early, so I created longer gaps and one gap where there wasn't one before (but it still reads fine).
[Cats are pregnant for about two moons, and this is half+half+half+half=two full].
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Alder "finding out" / thinking that Myrtle likes him romantically and also him realizing his own feelings occurs in the last half-moon.