I've had a pup in each of the last 4 years ... and I still forgot with my current 5 month pup! I drop meals down to 3 a day at around 4 months, and 2 meals at 6 months, or thereabouts. But, it just depends on the dog. My pup went to 2 meals a few weeks ago 'cause she just wasn't eating all her food at each meal time. However, I think that was more due to the fact that her back teeth were falling out! I've now reintroduced the 3 meals. Feeding the daily amount I want to put into her, on 2 meals it meant each meal was just a bit big for her to deal with. So, we're back onto 3 meals for another month (or maybe a bit longer) - the mid day meal is slightly smaller than the morning and evening meals - in preparation for when she's onto 2 meals.
My adult dogs get 2 meals a day, 1/3rd morning, 2/3rds evening. That's the way I've always done it and it's convenient to me. If you're planning to drop to 1 meal as an adult, I would be looking at doing that between 10-12 months.
Hope this helps.