Over 20,000 years ago - Sticks and bones
"Ice-age hunters in Europe [...] scratched lines and gouged holes in sticks and bones, possibly counting the days between phases of the moon." (NIST)

~ 3500 BCE - The Obelisk
With "bureaucracies, formal religions, and other burgeoning societal activities," humans "apparently found a need to organize their time more efficiently."
After the Sumerian culture, "the Egyptians were apparently the next to formally divide their day into parts something like our hours. Obelisks (slender, tapering, four-sided monuments) were built as early as 3500 BCE. Their moving shadows formed a kind of sundial [...]. Later, additional markers around the base of the monument would indicate further subdivisions of time." (NIST)

~ 1500 BCE - The Sundial
With "bureaucracies, formal religions, and other burgeoning societal activities," humans "apparently found a need to organize their time more efficiently."
After the Sumerian culture, "the Egyptians were apparently the next to formally divide their day into parts something like our hours. Obelisks (slender, tapering, four-sided monuments) were built as early as 3500 BCE. Their moving shadows formed a kind of sundial [...]. Later, additional markers around the base of the monument would indicate further subdivisions of time." (NIST)

~ 1500 BCE - The Water clock
After the obelisk, "another Egyptian shadow clock or sundial, possibly the first portable timepiece, came into use [...]. This device divided a sunlit day into 10 parts plus two 'twilight hours' in the morning and evening." (NIST)

~ 325 BCE - Clepsydra
The Greeks began using water clocks, which they called clepsydras (water thieves). "These clocks were used to determine hours at night, but may have been used in daylight as well." (NIST)

Late 9th Century - The clock ( first recorded mention)
Although the English credit Alfred the Great with the invention of candles graduated to mark the passage of time, in fact historical evidence suggests that candle clocks were prevalent in the orient prior to appearing in Europe. (Britannica)

1270 - First Weight - driven clocks
"In the first half of the 14th century, large mechanical clocks began to appear in the towers of several large Italian cities." (NIST, and Britannica)

Prior to the 14th Century - The Sandglass
Used to measure cooking-times since the middle-ages, sandglasses acquired wide-spread functional as well as metaphoric use being used to time the conduct of legal and commercial affairs, in the academic and ecclesiastic circles and even to measure the duration of torture sessions. (Britannica)

Late 15th Century - development of the first watches
Spring-driven clocks probably appeared first in Europe during the early 15th century and because they were small as opposed to their weight-driven predecessors, it became possible to construct timepieces suitable for domestic use. The potential for progressive miniaturisation allowed the emergence of watches. (Britannica)

1656 - The Pendulum Clock
"Christiaan Huygens, a Dutch scientist, made the first pendulum clock, regulated by a mechanism with a 'natural' period of oscillation." (Galileo Galilei is credited with discovering the principle of the pendulum-clock, which he began to study as early as 1582.) (NIST)

1920s and onward - Quartz crystal oscillators and clocks
The development of quartz crystal oscillators and clocks "improved timekeeping performance far beyond that achieved using pendulum and balance-wheel escapements." (NIST)

1949 - The atomic clock
"In 1949, NIST built the first atomic clock, which was based on ammonia."
("Atoms constitute a potential 'pendulum' with a reproducible rate that can form the basis for more accurate clocks.") (NIST)

1967 - The atomic second
"The cesium atom's natural frequency was formally recognized as the new international unit of time [...]: the second was defined as exactly 9,192,631,770 oscillations or cycles of the cesium atom's resonant frequency, replacing the old second that was defined in terms of the Earth's motions." (NIST)