SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'de346b953ed9746a511d6ec5a5dab42138275036a0f14907916f045a0b32a328' 
  AND token = 'tzxZ2tLISlfM+OdUy3GUFWbIWjh5ZzjtkNP9ClFx/g4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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