Hmm. Well, that kinda makes sense, especially if they are really thirsty plants. By 2:00 in the afternoon of a hot day, they have expired a lot of water, and I'm guessing the roots at that time of day take up new water very greedily. Tomatoes are full of water, and the fruit will literally take up more water than the skin can keep contained. The 'meat' swells from the water, and the thin skin splits from the internal pressure.

Or, if they are good and ripe and plump, and expanded by the heat of the day, the pressure of water hitting the fruit might be enough to cause it to split. I've noticed how good, ripe fruit, especially after a rain, will split just from the gentle handling involved in picking it and placing it in a basket.

You are in the north - do you know if determinate varieties are preferred where you live?

Janie