If the plants "look wilty" at the end of the day after a hot sunny day but
are healthy looking later in the evening or in the morning, it is likely a
transpiration (think that's the word) issue. When the evaporation rate is
greater than the absorbtion rate, the plant will look wilted but will
recover as soon as the sun is down and it has a chance to "catch up" with
the evaporation rate. Or so I've been told.

So you're saying that if the tomato plants look "slightly wilty" almost
every afternoon at 3pm, but perk right up (without additional watering) by
6pm, this does not harm them or reduce production?

Cheers,
Stephen