You lose, you don't snooze
I once ended up having to select a very early departure after I'd selected the more civilised flight time I wanted but backed-out of it when my indecisiveness kicked in. When I went back I assumed someone else had taken the last seat but actually it was me keeping the seat I wanted from myself. I didn't realise until after I'd completed the purchase and then found the flight I wanted was still in a 'basket' from the earlier session. Oops.