Combine salt and saffron. Place one lemon slice in bottom of a wide-mouth 2-cup glass container. Sprinkle with a dash of salt mixture. Repeat layers with the remaining lemon slices and salt mixture. Cover and let stand at room temperature 3 days.
After 3 days, press the lemon slices down with a spoon. Pour the juice and oil over lemon slices. Place a ramekin, custard cup, or clean decorative stone on top of lemon slices (to weigh them down). Cover and let stand at room temperature 5 days. Remove weight, and cover with lid of container.
Note: Preserved lemons can be stored at room temperature for up to a month or refrigerated for up to 6 months.