SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '57239748551a640b797239415678328b84f002cffc6b7f22b97d3fa156bafed6' 
  AND token = '5BCDmqth6yjTE2nyfzUL4VelRvscZ8ZvBOuoDZAxHCk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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