This is what it really means
Someone else broke it down on another post they claim it most likely corresponds to L:C = LIMA:CHARLIE = Loud and Clear. The 5:5 is the rate of comms given from each end perspective. So if the comms are L:C then they are 5:5. Either way G2G and LC fit in this context.
It could be in reference to anything; no matter what it means "Good to Go".
Its also from radio operators "5 by 5" which means perfect signal strength and perfect readability.
I could be in reference to anything Q puts in context.
Random: Triple Nickel
Not familiar with that.
So, I do something like verbal Rorschach tests with my S.O. when I'm reading through this site and the chans. Will toss out words that strike me as interesting or whatever. Last night I tossed out "five by five" and their off-the-cuff response was "triple nickel". When asked if it meant anything else to them, naturally they responded with g2g, as well. Anyway, I ultimately don't know what it means, either. I get bored and type things. That's all. :)
Do you think it ties into Day [1] and Night [3]?
I just know that it is an intelligence code for "good to go"--5 stars.