A study of 800 million tweets has found that analytical thinking peaks at 6am - with people changing to a more emotional and existential tone in the evening.
The research, by the University of Bristol and published in the journal PLOS ONE, involved the analysis of seven billion words used in 800 million tweets.
Twitter content was sampled every hour over the course of four years across 54 of the UK's largest cities to determine whether thinking modes change collectively.
Researchers in artificial intelligence (AI) and medicine analysed the aggregated and anonymised content using AI methods.
They revealed different emotional and cognitive modalities in people's thoughts by identifying variations in language.
This was done by tracking the use of specific words across the sample that are associated with 73 psychometric indicators and are used to help interpret information about thinking styles.
Words and language at 6am correlated with a more logical way of thinking, with people changing to a more emotional and existential style in the evenings and nights.
Professor Nello Cristianini, the project lead, said: "The analysis of media content, when done correctly, can reveal useful information for both social and biological sciences.
"We are still trying to learn how to make the most of it."
The team found there were just two independent underlying factors that explained most of the time variations across the data.
The first, with a peak expression time starting at about 5am to 6am, linked with measures of analytical thinking through the high use of nouns, articles and prepositions.
Other studies have linked the use of these to intelligence, improved class performance and education.
Researchers found this early-morning period showed an increased concern with achievement and power.
The second factor, with a peak expression time starting at 3am to 4am, linked with the language of existential concerns.
There was "strong evidence" that language changes dramatically between night and day, reflecting changes in concerns and underlying cognitive and emotional processes, the researchers say.
"These shifts also occur at times associated with major changes in neural activity and hormonal levels, suggesting possible relations with our circadian clock," a University of Bristol spokeswoman said.
"Furthermore, the study revealed both cognitive and emotional states change in a predictable way during the 24 hours."
Professor Stafford Lightman, of Bristol Medical School, said: "Circadian rhythms are a major feature of most systems in the human body, and when these are disrupted they can result in psychiatric, cardiovascular and metabolic disease.
"The use of media data allows us to analyse neuropsychological parameters in a large unbiased population and gain insights into how mood-related use of language changes as a function of time of day.
"This will help us understand the basis of disorders in which this process is disrupted."
The paper, Diurnal Variations Of Psychometric Indicators In Twitter Content, is published in PLOS ONE.