The short answer
There is no fixed schedule. In a hot spell, check the soil every day. A bed that normally needs water every few days may need it every day or two. Shallow-rooted, leafy crops and containers dry out fastest.
Water deeply, not daily-and-lightly
A deep soak that reaches the root zone encourages roots to grow down, where the soil stays cooler and damper. Those plants cope with heat much better.
A quick daily sprinkle wets only the surface. The roots stay shallow, and the plants suffer the moment you miss a day.
Water early
Early morning is the best time. Less water is lost to evaporation, and the leaves dry out before evening, which helps keep fungal problems away.
Mulch
A layer of mulch, such as straw or compost, keeps the soil cooler and slows drying. In hot weather it can noticeably stretch the time between waterings.
Signs your vegetables are thirsty
Wilting in the afternoon heat that recovers by evening is often just the plant coping with the sun. Wilting first thing in the morning is different. It means the plant needs water.
Uneven watering causes its own problems, such as split tomatoes or leafy greens running to seed early. Steady, deep watering is kinder than feast and famine.
Rain still comes first
If a real soaking is forecast, hold off. See should you water the garden before rain? for how much rain counts.
What Agent Aqua does
Each zone has its own spacing between waterings, estimated from the plants you grow in it.
Agent Aqua treats a forecast high of 30 °C (86 °F) or more, and especially 35 °C (95 °F), as a reason to water, as long as there hasn't been meaningful rain. In a very hot, dry spell it can bring watering forward sooner than that zone's usual spacing.
The rain rules still win: if a soaking is due, it skips. It also knows which hemisphere your garden is in, so "summer" means your summer. Each morning's report gives the reason for each zone, such as the temperature that decided it.
To see the full picture, read how the daily check works.