SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'f21810300fbeed9fbf78662883e22af9b4d44dac1437c382d51f9941ed3939b6' 
  AND token = 'fC/QGJO5mTDohF1KbAJ8wbI/O+ZrBHtAr7NDhjd/Gzc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}