Re: "turn over (two words) a new leaf in my life"
Is this correct? "Its about time to turnover a new leaf"
Yes - but use two words. And it's not necessary - as your title does - to add 'in my life'; if you
turn over a new leaf your life changes.
Incidentally, the 'leaf' in the metaphor is a
page - you could also, when you make a change in your life, describe it as 'starting a new page/chapter'
[one or the other].
b
PS A
turnover - one word, stressed on the first syllable - is noun.