Is it true.... Testing with OPK's b4 period..???

Hi everybody, af due today, I told
​Myself I wouldnt buy hpt until today. I used a opt this morning and got a strong positive straight away.... I've read mixed messages on doin this, I just wanted to know what you all think...
​But yes needless to say I will b goin out n buying a test today if af doesn't show ... Tia and GL..