Throughout East Africa, there is very little variation during the year in the time of sunrise and sunset. There are twelve hours of daylight and twelve of darkness. Therefore time in Swahili is measured from daybreak and sunset as was the custom in Biblical days. Since the sun usually rises at about 6 am, 7 am is the first hours of daylight. Similarly, the sun generally sets between 6 pm and 7 pm, so that 7 pm is the first hour of darkness. This means that Swahili time and ‘Western’ time are just 6 hours different. That is you would add or subtract 6 hours from ‘Western’ time to get Swahili time.
For example 9 am in ‘Western’ time would be hour 3 or saa tatu in Swahili.
Although Swahili time is always 6 hours different from ‘Western’ time, most Africans set their clocks and watches to ‘Western’ time, and read it off automatically in Swahili time.
Africans who live outside the larger towns are extraordinarily good at telling the time even without a watch or clock. A glance at the sun and their shadow is sufficient for them to gauge the time to within an hour, and more frequently to within half, or even a quarter of an hour. If the day is overcast, then their accuracy diminishes.