目前可以更新了，但是時間會因為偵測而延遲數秒更新
謝謝dark angel的幫忙

最後改好的程式碼如下
import RPi.GPIO as GPIO
import Adafruit_DHT
import I2C_LCD_driver

from time import *
import time
mylcd = I2C_LCD_driver.lcd()


while True:


humidity, temp = Adafruit_DHT.read_retry(22, 4)
mylcd.lcd_display_string("Time: %s" %time.strftime("%H:%M:%S"), 1)
mylcd.lcd_display_string("Date: %s" %time.strftime("%m/%d/%Y"), 2)

mylcd.lcd_display_string("temperature: %.2f C" % temp, 3)
mylcd.lcd_display_string("Humidity: %.2f %%" % humidity, 4)