These are the 2 schools of thoughts for determining the start of Asar prayer times
These 2 schools of thoughts use different criteria to determine the start of Asar prayer. They do not affect the timings of the other prayers.
Shafi: The start of Asar is when the shadow of any vertical object exceeds the length of an object
Hanafi: The start of Asar is when the shadow of any vertical object exceeds twice the length of an object
Usually Hanafi Asar time is approximately 1 hour later than Shafi Asar prayer time.