There's no lock. You can unstake any amount at any time, and your SOLC goes back to your linked wallet. Three rules are worth knowing first.
1. Pending rewards can be forfeited
Card rewards stay pending for about 7 days after you spend. If your tier drops below the tier that earned a pending reward before it becomes claimable, that whole reward is forfeited. This includes a full unstake.
Partial unstake that keeps your tier: nothing is forfeited.
Unstake from Private to Signature: rewards earned at Private that are still pending are forfeited. Rewards earned at Signature stay.
Full unstake: every pending reward is forfeited.
Claimable rewards are always safe. They're yours even after you unstake. The unstake screen shows exactly what you'd lose before you confirm.
2. When staked SOLC counts
SOLC you stake counts toward your tier straight away.
In a few cases it can take longer: SOLC added soon after you unstake can take up to 7 days to count. The rest of your stake keeps counting the whole time.
Accounts linked to another account that staked first (for example, by a shared device) can wait up to 30 days.
3. Your tier follows your stake within minutes
Free cards, Drops multipliers, staker-only drops, no-fee withdrawals and card rewards all use your current tier, and a lower stake lowers it as soon as we see the change on-chain.