SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6c736aafca4a8f2dd43705360485690308cddabccffe386a0d84da87e9e31a88' 
  AND token = '3qnjVutBECYSrYFRGnt9mT7wfP9xDq2EOp0UgU9cXpg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00042

JSON explain

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