Tomato plants should get a quart a day without fruit and 1/2 gallon a day with fruit.
There are very few hard-and-fast rules in gardening.
As with so many other guidelines to taking care of our plants, adding water depends on the dampness/dryness of the soil they're planted in. If the soil retains water, simply pouring X amount of water onto the plant's roots because of a rule could lead to over-watering. OTOH, if the soil is sandy and very fast-draining, such amounts of water might not be enough, especially during periods of very hot temps.
Check the soil about an inch down using the low-tech instrument known as "the human finger." Poke "the human finger" directly into the soil down to the first knuckle and assess the moisture content of the soil. If it's dry, then add water. If it's moist, don't add water. Perform this measurement daily at approximately the same time (e.g., morning, mid-afternoon, or evening) each day and become familiar with what your plants require.
Side benefit: Daily checking will also give the gardener early warnings of enemy incursions (destructive insects, diseases, etc.) and welcome bulletins that reinforcements have arrived (ladybugs, praying mantises, other beneficial insects and pollinators).
Sunset Zone 17, USDA Zone 9