Isolation times start from the start of your positive test date only if you remain asymptomatic throughout the isolation period. If you initiate isolation from your test date and then you subsequently develop symptoms, your 5-day isolation and 5-day masking period time restarts from the first day of symptoms. If symptoms develop, you must also be free of fever (without using fever-reducing medication) for at least 24 hours AND symptoms must be improving to end isolation.
“As much as possible, stay in a specific room and away from other people and pets in your home. If possible, you should use a separate bathroom. If you need to be around other people or animals in or outside of the home, wear a mask. Tell your close contacts that they may have been exposed to COVID-19. An infected person can spread COVID-19 starting 48 hours (or 2 days) before the person has any symptoms or tests positive. By letting your close contacts know they may have been exposed to COVID-19, you are helping to protect everyone.” -CDC