When is a good time to be candid?

…and tell a possible Dominant/sub that you have an illness, although you work constantly on it as everyone does their health, taking care of yourself, yet it is something which must be told for choices to be made or a relationship to further.
I have just started making a connection with a seeming wonderful and kind Dominant and I feel/think this is now the time, before things go further. I will always have this illness and it will crop up once in a while, it will touch both of us even if slightly - so I feel it is something he should know and decide what he wants before we connect more or get too involved.