This depends on your subscription plan (you can see more details about our plans and pricing here: https://ahrefs.com/pricing-plans).
Users of both Advanced and Agency plans get updates of their tracked keywords every 3 days. The Standard Plan allows our clients to see updates every 5 days. And the Lite Plan provides weekly updates. (See the screenshot below.)
You can also check this in your subscription limits (under Subscription Plans):
Please note that we don’t provide an ‘update on demand’ option at this moment, meaning you can’t force-run our keyword rankings checker to get updates more frequently than it is allowed by your subscription plan.