The short answer is: it's updated all the time, and it's dependent on the popularity of each keyword. 

The more popular a keyword is, the higher the search volume, the more frequent will be the update for the relevant data relating to a keyword search.

The data we are referring to here includes traffic potential, search volume, keyword difficulty (KD), SERP features and position on SERPs. 

Please read on for the full explanation.
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The Ahrefs' Traffic Potential shows the sum of organic traffic that the #1 ranking page for your target keyword receives from all the keywords that it ranks for. Values are cached and might differ slightly between reports.

The Volume metric shows how many times per month, on average, people in a given country search for your target keyword. In Keywords explorer we use the 12-months average.

Search volume and CPC are updated once a month. 

KD metric is dependent on the position on SERPs and hence updated once in a few days to once in 1-2 months (depending on the search volume for the respective keyword).