At 12:30 to 1:00 on a Saturday (and 3-day weekend for many), I would seriously consider taking Uber/Lyft from your Harbor hotel around Katella to the Grand Cal/Storytellers. Should just be a few $$.
If you have absolutely no bags (And I mean zero, including purses), there may be a no-bag line that you can fly through. Or, you could scope out the bag-check lines and, if really bad, retreat to the DL Uber/Lyft area and score a ride instantly.
Logic:
As said, bag check can be really long mid-day and it's not very magical. You will enjoy arriving at the Grand Cal front entrance and entering the lobby through the sliding doors, to Storytellers. Then, on your return, the bag check/security exiting the Grand to Downtown Disney should be near-empty. You will have a nice walk through the Esplanade back to your hotel (or parks).