relitive time

I've been thinking, what is time? a unit of measure I know. but how can it feel so different, go by so fast, tick so slowly. can we change it? affect it? or is it set, the one thing in my world set in stone. is it really the independent variable of life or dependent on something else? I don't know, I'm feeling philosophical, nostalgic, lonely, somethings i can't quite put my finger on. Can someone explain it, does it matter, do i care?