Chronobiology research has moved on from the simple 'morning is best' claim. The current evidence is more specific: cognitive performance varies by time of day, but the direction and magnitude of that variation depends significantly on your individual chronotype — whether you are naturally a morning person or an evening person.

A systematic review published in the journal Chronobiology International (2025) found that for morning-type individuals, peak cognitive performance occurs approximately three hours earlier in the day than for evening types. Research published in PMC found that simple attention and working memory both peak around 10 am — but this finding applies most strongly to morning chronotypes. For evening chronotypes, performance on equivalent tasks is better in the late afternoon and evening.

For UPSC specifically, there are two practical considerations that cut across chronotype:

First, the UPSC Prelims and Mains examinations are held in the morning (typically 9:30 am onwards). Evening chronotypes who do all their studying at night and never practise answering in morning sessions face a real synchrony penalty on exam day — their brain is being tested in its suboptimal window. This argues for at least some morning study sessions, particularly for mock tests, regardless of personal preference.

Second, both chronotype groups show a post-lunch dip in alertness (roughly 1-3 pm), making this a poor time for primary reading of difficult material — better used for revision, current affairs, or light tasks.

The practical advice: identify your chronotype honestly, schedule your hardest cognitive work in your natural peak window, but train yourself to write mock answers in the morning to simulate exam conditions.