The fruit needs about 5-6 months from flower to mature, which is defined as 8.5 Brix (% sugar). If you have only one it may get to be the size of a coffee cup (1/3-1/2 lb).
If it bloomed in March, it will be ready to harvest first of November; you can leave it longer, as the longer it stays on the tree the more yellow it will get, but it won't get "riper", only more colorful... some of that depends on your climate and how cool your nights are.

I would recommend you don't leave it on the tree past the end of December, as it will retard the next bloom.