Certified GKH Gardening Expert
Once you see flowering, it is an early sign that fruit will soon follow. This could be 1 to 3 years, but it is usually fairly soon after the first flowers.
You can give it a boost by giving it a citrus fertilizer. This will give it the nutrients that it needs to properly produce fruit.
This article will give you more information on the care of these: https://www.gardeningknowhow.com/edible/fruits/tangelo/tangelo-tree-information.htm