Aside from everything Leslie has said, the only thing I can think of to add is:
Built close to each other,
what fits in between?
Out of the TRS Leslie found, the letter T is the only one that fits inside the word "between".
What fits in between
has been found before
Leslie found T in his/her solution.
But one was different,
and is waiting for more
Since Leslie's solution was TRS, and the riddle was specifically looking for T, it's different. It's "waiting for more" because it wants to be noticed in the word "between".
It's not only a symbol
Both "T" and "t" are used as various symbols, marking perpendicular lines and the Christian faith.
but like a small lagoon
Rising from the dead
Not sure? Maybe the fact that "T" isn't present in "morning", but reappears each day in the "afTernoon" and stays throughout the "nighT". Ooooor it's referring to "afternoon tea"...
Bobbee's original comment was something like
"There's going to be golden rain in two days." -- "Golden rain" referring to "ti", a drop of golden sun, and "in two days" being literal -- "in Two days".
Other potential clues that probably aren't clues but are most likely just me being paranoid about everything being a clue... clues.
The title, twofold. "Tear 'it' apart". If you take it apart, you're left with an I and a T, or literally the phrase, "I, T" a la "I, Robot". Also, "One more time" -- the letter T is often used to denote (or countdown) time. So again, referencing T.
"The good disguise wins, so you act as twins". Aside from somehow (though I'm not 100% sure how) pointing to U, this could also be saying that "wins" is a good disguise for T, like when used in "twins".
"Two towers of letters" could refer to the "two towers" in the middle of the word "leTTers", although I'm not sure, since the "l" also looks like a tower.
Actually, that said, "Tear it apart" to get T, then "one more time" to get another T... Along with the repeated "Two Towers" references, the fact that it's "waiting for more..." That could mean that the answer is actually TT? ("TT" does "fit in between" the "leTTers" too) And, incidentally, "TT"could be construed as looking somewhat like a lagoon. shrug
Uh, ok so.
Two towers of letters, what fits in between?
What fits in between has been found before. But one was different and is waiting for more.
I can't tell you how many letters we've found already. "T" is different in that it occurs twice in the word "letters" (albeit so does E, but it wasn't in the RST tower).
It's not only a symbol but like a small lagoon. Rising from the dead every afternoon.
This just goes on to further describe which of the letters is "different". So yeah, my final guess is "LETTERS".
If that's not it, then I'll wait for someone else to get it so I can punch myself. :D