Early starts make sense because the sun gets strong fast, and by midday everyone hunts for shade or a cold drink. Then a short, heavy shower rolls through, the streets steam, and the evening opens up with food stalls and night markets.
The climate is equatorial, hot and humid all year, with two monsoon seasons that send rain to the east coast and Borneo in one half of the year and to the west coast in the other. A Local Friend tells you when to go early and when to linger, so the heat and the rain simply fit into a good day.