When to OPK on Clomid????

[Tigerlilies]

Hello ladies, I've MC twice this year so we're trying clomid for the first time in hopes that the problem lies in the egg not fully maturing before dropping. I usually O CD12 (cycle length usually 24 days), I'm on CD10 today started my Robitussin to thin out the CM. I know from previous postings that clomid can make you O later. I have 9 OPK's left and I really don't want to buy any more unless I have to for next month. If I start today, I'll have enough to test up to CD18. Should I go ahead and start testing today in case clomid doesn't change my O day or wait one more day b.c it most likely will be pushed back????