If you fail to use a ticket on the first day of its predeclared lifespan then you can still use the ticket during the remaining days of its lifespan with no special treatment.
If I remember correctly the life span of a 2018 or 2019 vintage 7 day ticket is 10 days.
If you want to get back the missed calendar days for use on the back end then go to the ticket booth and "upgrade" the ticket declaring a new start date. I would expect that the upgrade cost would be zero dollars if a brand new ticket purchased for your new desired start and end dates has the same or lower price than the original ticket.
Now if you are daring you might procrastinate on the above upgrade until after the ticket rejected itself at the park gate before you thought it would, proving that the gate software is now smart enough to identify a ticket priced for a cheaper span of days being used for a more expensive span of days.
Because the one day ticket price of every individual calendar day can differ from that of the previous or next day, the price of an X day ticket starting on any given calendar day can be different from the price of the same kind of ticket purchased for the previous day or for the next day as the starting day.