1. I think "trendsetting on reality" is a reference to reality TV shows. If you're trendsetting on reality TV, you're becoming famous and setting new styles/changing people's minds. But, "trendsetting on reality" has no clear meaning. It isn't a phrase that is normally used in the English language. 2. An existential crisis is not about aging, it's about the meaning of life. But, in this case, the word 'time' is inserted into the phrase. So, it sounds like she means that she is questioning the meaning or existence of time or the time she has spent living. Like the answer for your first question, this is open to interpretation, because "existential time crisis" has no clear meaning and isn't a phrase normally used in English. 3. I think this refers to negative thoughts and bad memories creeping back into her mind. There is an idiom like, "Dark thoughts are gnawing away at my mind." Rats gnaw on things. So this is symbolic for thinking a lot about negative things. 4. "I'm hardly sanctimonious" means that she is not at all sanctimonious. She's being sarcastic when she uses "hardly" to mean that she is not at all sanctimonious. This type of music is full of symbolism and odd turns of phrase. If you like it, it's a fun way to learn a language, but be aware that most phrases used in music are not things we would actually use in our daily speech.

1: I don't know. 2: No, I don't think it has anything to do with getting old. It's probably more that she doesn't have enough time to do what she wants to do (daylight savings won't help) , or possibly that her times are all messed up. (e.g. sleeping during the day and awake at night) 3: No, it's not idiomatic. I think it's a suggestion of mental disease. 4: No, it means she is far from sanctimonious. 'I'm hardly' is a common expression meaning that. e.g. in my case - 'I'm hardly a fluffy songwriter'. ;p