It's everyone's personal choice when to talk about diabetes and to whom - whether it's starting a romantic relationship or, for example, joining a new work or hobby community. However, it's good to be aware that usually bringing up the subject as early as possible also gives the other party the chance to get used to the idea and reduces the stress associated with you talking about it. Early and open disclosure also increases your own safety, as people around you will know how to recognize possible changes in your well-being and react appropriately.
However, you don't need to share all the information at once; you can and should talk about it gradually, just as in the beginning of a relationship you gradually share things about yourself with the other person. In the end, diabetes is just part of the diverse whole that you are, and which the new person gets the joy of getting to know at the start of a relationship. While it's good to clarify the basics early on, you can take your time to deepen their understanding at your own pace and to the extent that you feel comfortable.
Often, you may wonder and worry about how a new partner will react to the news of diabetes at the start of the relationship. However, this shouldn't be overly worried about, as people generally get used to new situations and things, even if they initially are surprised or scared by them, as long as they have time to adapt to the idea and get sufficient information. Reliable information increases understanding, and it's always easier to relate to what is understood. The goal of dating is usually to get to know a new person and feel out whether this person could be someone with whom you could share your life for a longer time. Both parties should focus on each other as wholes, in which diabetes is just one piece.