There is no definitive total number of tests that can run on a Hardware Private Agent. There is, however, a limit to how many tests can run at the same time.
According to our Network Engineers, Hardware Private Agents (hardware installed at a client site) run multi-threaded software. Depending on the specific hardware of the Agent itself and the type of Agent, the Hardware Private Agents can run between 10 and 16 tests (threads) at a time.
Once a test is finished, the process is killed, and a new test can start immediately. How many tests run over an hour depends on the size and complexity of the tests (more single-page tests can run during the same interval as a complex script, for example).