Writing takes more time into memory compared to reading, because when data is sent / written into memory, before the write operation takes place the memory check is done to verify its content, it needs to erase the content if it exists and then write the data, for reading it uses less time because it fetches the data directly from memory.
writing data into internal registers also works in same way.
even if there is no data a check is done for presence of data which takes little extra time compared to read operation