1. Combine potato and 11/4 cups water in a microwave-safe dish. Microwave at high 8 minutes or until potatoes are tender. Set aside.
2. While potatoes cook, combine remaining 1 cup water, clams, thyme sprigs, and bay leaf in a Dutch oven; bring to a boil over medium-high. Cover, reduce heat, and simmer 6 minutes or until shells open. Remove clams from pan using a slotted spoon, and discard any unopened shells. Strain cooking liquid through a fine mesh sieve over a bowl; discard solids. Cool clams slightly. Remove meat from shells, and chop. Discard shells.
3. Heat a medium saucepan over medium. Add bacon to pan, and cook for 4 minutes or until browned and crisp, stirring occasionally. Remove bacon from pan using a slotted spoon. Increase heat to medium-high. Add celery to drippings in pan; sauté 3 minutes or until tender, stirring occasionally.
4. Combine flour and bottled clam juice in a small bowl, stirring with a whisk until smooth. Add clam juice mixture and reserved cooking liquid to pan. Bring mixture to a boil; cook 1 minute, stirring constantly with a whisk. Add reserved potato mixture and 1 teaspoon chopped thyme to pan; reduce heat, and simmer for 5 minutes, stirring occasionally. Remove from heat. Stir in chopped clams and half-and-half. Ladle chowder into bowls; sprinkle evenly with bacon, remaining 3 teaspoons chopped thyme, and pepper. Serve chowder with oyster crackers.