You are safest in the afternoon my motto's always been when it's right, it's right why wait until the middle of a cold dark night when everything's a little clearer in the light of day and you know the night is always gonna be there any way.
There is really no way of knowing when the appropriate time is to not get pregnant. Try talking to your doctor ( Gynecologist) about when you are fertile. They should know. Please do not listen to anyone else that is not certified to tell you when it is best. They don't know squat.Once you find out when you are fertile have sex when your NOT fertile. And definitively use protection. And don't be stupid and do the pull out method. Use Condoms, Patch, Birth-control, shots. If you want to be safe. Have sex when your married. But, either way do what you think is right.
NEVER. Unless your married to a committed partner and you both have had physicals and you use birth control correctly. Or you've had a procedure to remove your uterus and can't get pregnant plus the above. Make a good decision.