SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b6c25624604c03042cb90bf571bd1a8f650dc9ab53409112e5bdeb115b444a51' 
  AND token = 'XM0HJZU2aR7qIAPOV5NfCpodEalY64f76oMRD5uSMtg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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