Ref. No. 40/
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
Minimum period of menses is 3 days and maximum period is 10 days. If bleeding stops before day 3, then the bleeding is due to infection, not of Haidh. And this kind of bleeding is named with Istihadha. A woman must act as normal, and perform namaz and keep fasting. In the above case, she has to complete the day 3 waiting. If the bleeding is seen on day 3, then all the three days will be counted as of Haidh, but if the bleeding is not seen on day 3, then the bleeding of previous two days will be considered as of Istihadha. And the lady must perform qaza namaz of these two days.
The maximum period of Haidh is 10 days. If she sees blood before day 10 anytime, then all the days will be counted as of Haidh. If the bleeding which stopped before day 3, starts again on day 11, then the past ten days are not of Haidh days.
And Allah knows best
Darul Uloom Waqf Deoband