Also called: 5-year clock
Two separate clocks. Earnings come out tax-free only after five tax years from your first Roth IRA contribution and age 59 1/2. Each conversion has its own five-year clock for the 10% penalty.
The conversion clock matters only before age 59 1/2: converted principal withdrawn within five tax years of that conversion is subject to the 10% early-withdrawal penalty. After 59 1/2 converted amounts can be withdrawn at any time.
Roth IRA withdrawals come out in a fixed order: regular contributions first, then conversions oldest first, then earnings.