I think the earliest that you can before any sexual lines are crossed. I know people have casual sex but if you do it’s still important to have that conversation with someone early. Never wait.
For anyone who takes on the responsibility of sex, condoms are number one. You must protect your own life at all times. Condoms are not 100% either. They break or can slip out-of-place, be vigilant. No one ever looks “dirty” as people used to call it. You must remember this is the age of information. It’s not dirty it’s about knowing your status and the status of your partner. If you are having casual sex you take on an incredible risk to yourself and someone’s life. Sex can kill you. You don’t have to be afraid but you do have to be vigilant. This is why I never tell married woman not to continue getting tested. I told my readers how a doctor told me that because I am married I carry a smaller risk of getting a sexually transmitted disease. In theory he was right in real life I will never take that chance. Love and responsibility are two different things. My quality of life can easily be interrupted by one slip of myself or my mate. Protect yourself at all times.
Do not let the heated moment of sex ever put your life at risk. Not everything can be cured with a pill or a shot. Don’t play Russian Roulette with your life. Know your status, speak up early, and wrap it up and married or not always know your status and constantly get checked!