SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '621587856fe46ce24820db8a95a68b0f9670928daf5afabc2317a85df48eae3b' 
  AND token = 'FDEZIIzNlF+eQRVambfOzSi+7UKs+6jL0dCk8HtM3oY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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