If there is good reason to suspect that local authorities are weighing closure of the mikveh, or that you or your husband are at risk of quarantine, then you should attempt to perform an early hefsek taharah on day four, as well as a thorough bedikah on day five. That way, should closure on short notice remain a concern, you will be able to immerse a night earlier than you ordinarily would, based on the early hefsek taharah (and counting the bedikah the next day as the first bedikah of the clean days). If the concern fades, then you will immerse on your usual schedule.
As you go through the clean days, you should keep two counts in mind: one based on the early hefsek taharah, and one based on the regular schedule with the day five bedikah counting as your hefsek.
If you typically perform a reduced number of bedikot, please consult with us to confirm how best to adjust your practice to this scenario.