SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a3140c2b970af592354113c03d2fed29158fc863da6d629d114efee52b06f951' 
  AND token = 'hR2g3Ml51ANW62nj5hzl9gR8EnJIoAIgBWjbZLreCUo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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