So if I decided on a night trip at 2500ft I can maintain this altitude for the whole trip irrespective of heading due to being below transition altitude
Yes, that's correct.
On the other hand, if you were above the transition altitude, you would have to follow the quadrantal rule, due to being IFR, which isn't the case if it had been a daytime flight. And, regardless of the altitude you're flying at, you must remain in VMC, due to the restriction on your license.
I know what you mean about "those days", but this seems to be a constant source of confusion, so rest assured that you're not alone!
FFF
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