When Nomorobo blocks a call, we send the caller to a captcha feature, which asks them to input a random two digit number. If the caller inputs the number we push the call through to the user. This is to allow any legitimate calls that are mistakenly blocked to be able to reach the user.
Unfortunately, that connected call has a time limit of ten minutes. In this situation, the user should report the number to be added to the allowlist. After this is done, the time limit will cease to be an issue.