When you analyze the same keyword alone in Ahrefs Keywords Explorer repeatedly, one credit for advanced metrics will be consumed each time. The reason is that the tool pulls out the freshest data for this keyword each time you request its analysis.
However, if you put two and more keywords into Ahrefs Keywords Explorer and analyze them all together, their data will be cached after the first analysis. So next time, the tool will show you their cached metrics and your credits for advanced metrics will be saved.
When you run out of credits, you will still be able to see monthly Search Volume and cached Keyword difficulty.
The credits for advanced metrics reset each month the day your subscription has begun. You can find the exact date of your monthly credits update in the ‘Subscription plan’ tab of your Ahrefs personal profile.