SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '55dddb73bf1a72b0eceee59643198934eede54ffaf92d5328392714158ba90f7' 
  AND token = 'K34/jK+6Pic023hvvJV7XqbcyU+/vH6c86JMVrDaiZ4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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