They must be used the same day. You can leave and come back later that day, but make sure the front desk person knows you intend to come back later in the day. If you forget, they can still fix it for you... just let them know and they will check it for you.
You keep the hours. You can come back the next day and use them.
To be honest that is a good questions I think you could call and ask but usually I think your just gonna have to take that lost of 4 hour
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