The plants probably enjoyed the heat the past few days, but I was so ready to welcome the rain today! Hooray, rain!
I used to avoid gardening before 4pm because it was just too hot. After speaking with a few farmers from the north, I now realize that my selfish reason for waiting until it was much cooler, was good for the plants too!
According to James Amparo, who is encouraging other farmers to use organic fertilizer, the best time to water plants is before 9am and after 4pm, (I'm speaking Philippine time here; can't really speak for other climate zones) to prevent "shock". This also explains why farmers get up really early to tend to the farm then "take a break" during the hotter parts of the day, then resume when the temperature goes down. Jhoey from Pinoy Organics has a pretty good analogy for it: A glass container kept in a freezer breaks when hot water is poured into it. James adds that if you see a plant that is withering, let it be, then only water it outside of the 9am-4pm window.
Plants do have an internal heat shock system, but they can only take so much stress. And let's not forget the gardener!