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
‘But it does me no injury for my neighbour to say there are twenty gods or no gods. It neither picks my pocket nor breaks my leg.’ - Thomas Jefferson