We talked about this in my microbiology class and one of my other classes it would take about 6 months for an accurate reading...I hope I helped.
You probably should use one yes unless you are ready to take the consequences of possibly having a child or getting an STD. I mean if you are truly in love and I mean truly in love I guess it might be okay not to but you really should unless you are married.
Honestly in my opinion unless you are wanting to take the consequences of std's and/or pregnancy use one, I mean if you are willing to take those consequences then it's up to you. But unless you are truly in love and I mean truly I would definitely use one.