SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51622935be175746c6757842f1fc9a39e89d7ecf012f650a3e7f81d076fffd84' 
  AND token = 'xVx8GJjW1jG3YgGfAfOLrywdaNnJciAzBCu4EsRuq50=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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