You're talking about double shifting. Depending on the facility and time of year you can double or rarely triple shift all week. My hub doesn't have a day sort but double shifting has been available all year between twilight and midnight sorts usually Monday and Tuesday sometimes Wednesday and Thursday but rarely Friday. Doing it a full week continuously would indicate bigger issues and outside of peak corporate would put a heavy hand down on local management to fix their staffing so that double shifting wasn't a thing anyone could rely on for more than a day here or there.
Edit: If you're worried about hours/money keep an eye out for sups working, even if they have people double shifting they will have sups work to make the numbers look better. Management will probably fight the grievances but at least here even with double shifting available people still get paid for the sups working grievances, albeit slowly.