Tomatoes- how often to water in this heat?

The ones in the poly tunnel get watered 3 times a day. The ones in the greenhouse twice a day and are not on trays. I wil put trays under them and then fill the trays with water as well as watering three times a day.
I have felt down in the soil and its just the top layer thats dry.

Mine are outside in flower buckets. They get around 2L once a day, even with the heat this has been enough to keep them moist until the following evening just, barring one or two days when it has been bonkers hot and windy and a top up has been required.