Would it help if you were to not think in terms of time or inches but in terms of results? Shove a long rod or rebar into the soil to see where it's damp and where it isn't. In "most" soils the rod will go in harder if it's dry. Don't worry about damaging the roots. Tomato roots are hearty. The gist is to give the plants water deep enough to encourage the roots to grow down to it.

Most people would agree that both excessive and erratic watering get you a poorer crop. Drip is very good once it's dialed in.

Drip irrigation is the best. You're doing that right. Keep in mind, however, that many drip irrigation hoses are not self regulating, meaning that the plants at the beginning may receive more water than those at the end of the line.
That being said, how well does your soil drain? Does it form pools of water on the surface?
If your soil drains well, then know this - tomato plants like to be flooded with water, but they can't sit in water for long. So I would turn on the drip irrigation system for an hour in the morning or night, turn it off, wait a half hour, then dog up a small hole about a foot deep ( be sure not to disturb the roots!!!), and grab a handful of soil. Squeeze the soil and see how it reacts. Is it wet, dry, crumbly, etc. Then adjust the water accordingly.

Thanks for the responses. The soil I have is a "triple mix" with one part manure, one part peat and one part top soil. It drains really well. When the drip comes on a small pool is present, which quickly drains after the irrigation is complete. Is it ideal then that the soil be moist, say six inches down, but not "wet"? Would a moisture reader be something worth investing in? My plants are doing very well with many already approaching six feet tall, tonnes of set fruit (first tomatoes in a week me thinks), but I want to have that 'only from the garden flavor' that you just can't get in a store.