Zest 1 Lemon with a micro-plainer. Squeeze the juice from that lemon and muddle the zest, juice, sugar, and 4 sprigs of Thyme in a pitcher. Cut the other lemon into wedges, and reserve for garnish. Add ice and gin to the muddled ingredients. Then add the tonic water. Pour into glasses and garnish with lemon wedges and remaining thyme sprigs.