Is there an item that lets you heal more quickly?

[unclekrusty]

If so, can it be obtained before fighting the Watcher Knights?

[Shade]

Yes, there's a charm that halves the focus time needed for a heal, called "Quick Focus". It costs 3 charm notches to equip.
iirc you can buy it from Salubra for 800 Geo, so yes, you can get it very early in the game.

[bee3001]

If you have access to the Crystal Caves, you can also try to get Deep Focus which heals slightly slower but heals 2 at a time. Combine it with Quick focus and it'll heal for 2 at the normal rate. The downside is Deep Focus costs 4 notches and combined with Quick Focus, you will need 7 in total and it leaves very little room for anything else.