SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b5c60b724ed0558912bbf9bc4655d325ff24cb492f4f2fd5ffb6ef8b9714627c' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00030

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}