That's a tough question, and one I don't think there's any hard and fast "rule" for. I have leukemia, I was diagnosed when I was 30. My ex and I split up when I was 38 and when I started dating again, I had the same conundrum. And the best I can tell you is that it was different for everyone. Some, I told right off the bat, some I waited a little while. I think it's something you definitely have to be honest about sooner rather than later. Obviously, you don't want to scare anyone off but you also don't want to get in too deep with someone only to have them running away screaming :lol: That may happen down the road anyway, as well. People think they're ok with it and find out they're not after all. Such is life. But, most relationships don't work out and end for other reasons.
I think you'll know, in your gut, when it's the right time. I think that after 3 or 4 dates, you kind of know whether the relationship might get serious. If, however, you're just dating to have fun and not looking for a relationship, then I don't know that you need to mention it at all.
I know, not much help, sorry about that. Don't stress too much, though. For as many dates I had after my divorce, I think only one wasn't ok with the leukemia. The rest were surprisingly ok with it.