If existence did NOT exist at all times, we'd need another word for it. Just as had been pointed out, an elephant is always an elephant, but things which are not elephant cannot logically be called 'elephant'. By the same token, that which exists must definitionally be in an existant state at all times. 'Non-existant' is semantically equivalent to 'non-elephant'.
Boru
Boru
‘I can’t be having with this.’ - Esmeralda Weatherwax