Change Date Auto In Excel based on system Date

Hi,
i want to make a custom date based on system date

for example
i put some Manual Date in sheet1.range("a1") = 20/6/17
now i want to change Date Auto in sheet1.range("a2") = according to system date System (Not Default date of pc)

today i added the date manual in sheet1.range("a1") = 20/6/17
while today's date is 20/7/17 (system date)

now tomorrow date should be in sheet1.range("a2") = 21/6/17
while tomorrow system date will be 21/7/17 or changed by user into anything like 21/8/17

now here is a question if someone will change the date of the system? this one will not affect the date of sheet1.range("a2").... this will update auto after 24 hrs as system date changes...no matter what date is system, if you change system date 20/7/17 into 20/8/17 then after 24 hours this will become 21/8/17 (if system doesn't connect to internet)

i think this is possible for experts

thank you